Ok, so I'm about to buy a new 2007 chevy Silverado 1500. It looks like they are sticking with an upgraded 4 speed tranny, while the 2008's will get GM's new 6 speed tranny. It's supposed to shift better and offer better gas milage. so im wondering if the new trannies are worth waiting for or should i just be content with the 4 speed. any suggestions?

This is a very interesting question. If you want 6 speed than wait but if you think it is going to magically get you a lot better MPG do not waste your time waiting. It still takes "x" amount of power to move truck down the road and making a engine the peaks its torque at 4000 RPM turn slower yet under load rarely improves MPG. To get a consistant real world improvements in MPG they need to get the weight out not ad more gears. You might site the 6 speed ally used with Dmaxs and 8.1 but those engines both have a lot of low RPM torque and peak powers at much lower RPMs and can play well with them while a 5.3 does not. One more thing, the new 6L90 does not have a drive gear in it while ally still does (1 to 1 ratio) because of its modular compound design and it remains to be seen how this more complex tranny will play out in the field and in HD usage (more to go wrong with it) and I would not would to be the one to "test" it in a new car until it has been around for a few years. The 07 4L65 is based on a design that goes back to 1981 and its quirks are well understood and easy to repair if need be. The 6L90 will be a whole new can of worm for a while. It costs them less to build the 6L90 because it requires less man hours (more robot hours which do not take breaks or get sick) and this is one of the main reasons for the switch. The 6L series was designed to be build by robots while the 4L series was not.

ahhhh...you seem very wise snoman...thanks for the analysis, you make very good points. if i may...i've heard many diff opinions on the effects of adding larger tires to your truck. is it really that big a deal to add slightly larger diameter tires (say going from the stock 31.6 in dia to a 32.6 overall dia tire) or is it negligable? thanks again.  

Some say I am not so wise. I look at the physics involved in this.  Back in the "old" days, trucks came with 3.73 or 4.10 gears and 29 inch tires or so and no OD and the ran well towing or not and lasted a long time.(you still see then on the road if they have not rusted away) Today the tires are bigger and the axle ratios are taller, trucks are heavier,  they have higher tow ratings (lower standards of performance) and they have OD too but the though the engines carry higher HP ratings too they generally have less usable HP at lower RPMs than they did over 30 years ago (I have been around for a while) which means they have to strain more to pull their loads and less efficently. I like the concept of a 5 or 6 speed tranny but how it is applied can be another matter. GM now ships 1500 trucks with 3.21 and 3.42 axle and with 31 inch or bigger tires you have a truck that cannot use OD under anything other than most ideal conditions because the effective gear ratio is to tall for load and engine and it down shifts frequently and "hunts" around a lot for the right gear. This hunting over time places a lot of strain on trannies valve body and internals as it cycles over time between gears. If you want a truck that has a chance to last a while and you want good overall performance order a 07 with a 4.10 axle ratio not a 3.73 because the 3.73 will not save you any fuel in the real world and the 4.10 will play better with 32 inch tires to because increasing tire size make effective gear ratio taller. With this combo your truck will down shift less and pull OD much better and yeild a truck with basically a 4 speed tranny with all gears usable, not one with a 3 speed tranny that has a 4th gear that is usable only under ideal conditions. I have included a few links below for you. First one is a axle ratio/tire size calculator and the second one is for a list of actual gear ratios in a GM trannies including the planned 6 speed automatic (where you will see that there is no drive/1 to 1 ratio in it) You will also see that it has a .67 OD vs a .7 OD in current 4 speed tranny but a deeper first gear together with a "drive" gear that is 1.15 to 1 which suggests to me that GM plans to maybe use a even taller axle ratio to create the illusion of even better MPG but the result will be a vehicle that when in OD will be so tall that it will be constantly hunting between 4th, 5th and 6th on the highway and not make any better MPG anywhere but on the test dyno. Ity also remains to be seen how the new 6 speed will hold up towing too since there is no drirect drive in it and it has to use reduction units in all drive ranges which in themselves consume a bit of power and generate a little extra heat as well vs a 1 to 1 pass through. There is no direct 1 to 1 pass through on the new 6 speed because it is easier and cheaper to build it without one from a design point of view.(the Allison 6 speed wisely follows the old school design and has a 1 to 1 pass through)   I think the 6 speed is more of a sales tool than anything else because a good 5 speed design would have worked fine. Whats next a 7 speed? The more complex the clock works, the easier it is to muck it up.  Sorry for getting on the soap box for a bit.  

Axle ratio/tire size calculator
http://www.snoman.com/HTML/axlecalc_5a.html

GM transmission gear ratios
http://forum.snoman.com/viewtopic.php?t=153

Damn snoman, is there anything you don't know? hehe...ok so if i decide to go with a good quality lift kit, not too big, probably just a 4 incher so i can fit some 33's on there, how do i figure out my new max towing rating? I'm sure it will be less but how much. I've been looking at the different tow ratings on the manufacturer website and the different tow packages and 4x4 packages and in some cases it seems to be only a matter of installing bigger shocks is all they do to get a greater rating.  so if i go with a lift and get some good shocks and even put in an air ride suspension in the rear, I'm thinking most of my towing capacity should be preserved, save for the larger tires obviously.  your thoughts?  

No need to get cute about it. While you can restore the towing power part of it with IF you properly regear the truck after you install bigger tires there are other factors involved. You loose braking abilty with bigger tires as the increased leverage over the braking surface that a larger diameter tire provides makes brakes work harder giving you less overall braking abilty and reserve to stop extra weight. You might tow a trailer with brakes okay but if brakes on it fail you still have to stop it. (I have had this happen twice in 30 years) Then there is the extra strain the bigger tires place on axles that is never considered. If we are talking about a GM 1500 the rear end they use basically started life in a 6 cyl Nova and should have been replaced long ago because trucks have gotten heavier, tires bigger, GC's higher but rear axle is still basically the same design to save cost.  Next there is the suspension and frame. Detroit has been increasing towing ratings while putting lighter springs on each new generation truck to make them right more like cars and basically make them a car with a truck body on them. What Detriot rates stock 1500 to tow is down right scarey sometimes and they can do it because there is no federal guide lines on what is acceptable. GM rates a new 1500 to tow more than my 2000 K3500 can, GET REAL!!!. If you honsetly want to try to figure out where you are with your, take factor towing rating and first subtract at least 35% or more for a stock LD 1500 truck. Next if you have oversized tires, subtract 10% for each increase in tires size if you do not regear. On handling, when you raise CG on vehicle up in air more it reacts differently to towing and shocks with not fix this as it is a combination of frame, suspension, height and tires that effect stabilty. Sure you can move a heavy trailer if all goes according to plan and ground is flat but when you tow you need to be prepared for when things do not go as planned and emergency manuvers which can get pretty nasty with a lifted 1500 truck towing a a few tons or more. Maybe some think I am too conservative but I error to safety and I do not consider having to use 2nd gear normally on a highway grade as acceptable operation because when you have to you have exceeded your towing abilty power wise as vehcile is geared and engined. One more thing to try to tow with 33's on a 1500 truck with 3.42 or 3.73 gears is plain foolish. You want at least 4.10 to give you the basic equivelant of stock tires with 3.73's effective gear ratio wise which should be considered the minimum towing combo to begin with. A 3.42 is not a tow gear for more than 2000 lbs or so in a stock truck no matter what ratings say.

Yeah i tend to err on the side of safety too. I don't like surprises especially when towing or something to that effect. and if there is one thing i hate, its when manufacturers skimp just because they think "most people won't be taking their trucks or suv's off road". I like my stuff to be over-built so i know i can depend on it. Well even though I'm partial to GM, I'm not married to it. I had a ford when i was in highschool, and sure as hell dont want another one. What are ur thoughts about the Dodge Rams?  

Well I used to think kinda highly of them until several years ago. Since Dahmer bought them out the trucks and Jeeps and becoming more car like every year. Something I find particularly troubling with them since 2003 is the front drive axle design on HD and LD trucks. I will try to explain further. On HD trucks Dodge stopped using the D60 because of early failure of pivot joints with CTD engine in truck. The fact that they switched to a different axle is not bad in concept because the replacement axle made by AAM looks VERY sturdy amd it also shares the ring, pinion and basic carrier design (no disconnect on it though like GM has) with the GM 9.25 IFS.(dealer will not tell your that) The problem is the Dodge/Dahmer in their complete lack of wisdom had new axle designed with no disconnect when it 2wd and a bastard hub design (that is a recycled from the 70's) that prevents the installation of hubs to disengage axle (there is a aftermarket kit out there that is about 2 grand just fr parts to convert it to a lockout hub design)  Dodge could have easily had it speced with lockout hubs but choose to save a few buck, ad a lot of extra wear a tear to drive axle(because it is always turning powered or not) and make no mistake some loss of MPG.  This is kinda why they usually come in last in real world MPG on gas 4x4 models today. On 1500 trucks with IFS, they did a simular cobbed up setup. They used the "pig" (a AAM 8 inch) designed for a rear wheel drive IFS that has no abilty to disconnect anything in 2wd (because it was made for a rear axle) and installed it in the front so that in new Dodge tradition the axle is always turning too (ring, pinion, axles and driveshaft) With a GM 7.2, 8.25 and 9.25 IFS, the front axle shafts do turn all the time but not the ring, pinion or driveshaft in 2wd. Sorry if a seem a downer but I tend to be critical of 4x4 designs since I have been messing with them for over 35 years now and I tend to look down on what I cosider to be bad designed.  As a truck if dodge would loose the big bubble nose that limits visabilty up close and designe a other wise strong axle with lockout hubs they would go up several steps on my rating ladder.(you can disengage Tcase but the compleete front axle is ALWAYS truning on Dodge) Ford SD's may well be the last of the real "trucky" trucks left today.

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  The SnoMan
www.thesnoman.com

Yeah I'm afraid its usually about the bottom line these days. I was reading and suv test the other day for one of the magazines truck or suv of the year and the new tahoe and yukon actually got beat in off road drivability by a Mercedes. But oh well, what can i do? There was another thing i was curious about. I've been seeing alot of leveling kits for owners of trucks who dont want to go with a lift but want to level out the look of their trucks. so the kit usually raises the front about 2 inches and leaves the rear alone. I think its just 4 new shocks and maybe some spacers they are using to level it out. My question is, does the front track width shrink a little when the A-arms are cycled down further?

Cause if you think about it, when the suspension cycles up and down, it doesnt do it in a true vertical line, its more of a very slight curve, and with a longer shock, i would think the A-arms would be sitting lower obviously and thus would be lower on that curve so the track width would be slightly smaller. I'm not sure if i did a very good job of explaining it but do u know what i mean?

You are a thinker for sure and have a good head for this. Yes you are correct but how much realy depended on where you are at on the lower control arm radius and ususally the upper control arm is of a different length which means the as the axle drops is can change the chamber angle on the front spindle/wheel (tire tipping in or out at top)  which when done properly as the suspension extends the camber goes negative (top of wheel tipped in) which forces tire out at the same rate it is being pulled in of lower control arm radious so that the net result in very little shift in tread width  within a certain range of motion which helps handling especailly on bumpy roads. Do you follow me here or did I loose you?

Yeah i follow. I'm probably gonna go with a New GMC 1500. I saw em today at the San Francisco international auto show, they were lookin pretty good. and they had the new tundra there too, man, have you seen how tiny their rear axles are? is that legal? it looks like it should be on a civic or something. why do the japanese think they can get away with that stuff? I mean i guess it could work if it was made out of diamonds or titanium or something. its scary to see something that skinny on a truck that big. and i dont know what was up with the new Ford SD, but they really chopped that thing up...  

Do not let the size of those axles fool you as looks can be deceiving. Toyota uses a much higher quality steel in their axles that pound for pound is about 50% stronger than the steel Detriot uses in theirs and a strong basic design too. You will see a lot more broken and bent rear axles in a 1/2 ton Detriot vehicle than a Toyota. Off all the 1/2 ton trucks made in Detriot, GM has one of the weakest with the old 10 bolt that started life in mide size cars in the 60's with much smaller tires too. It should have been replaced years ago but GM has kept. Funny thing is they have a axle that you could replace it with (the 14 bolt 9.5 inche semi floater) but it cost less to use the old 10 bolt.  Lots of 10 bolts have bit the dust with lifts and big tires as there is little reserve in that axle as used.

are u serious? See stuff like that makes my blood boil. Why Detroit cant just make some simple changes to unsure superiority, i dont get it. well on the website, http://www.gmc.com/sierra900/1500/specsExterior.jsp   under MAX Trailering Package it says that they use a 9.5 inch rear axle. could that be the same 14 bolt axle you are talking about? And what do u think about the new Tundra? Should i give it serious consideration? And by the way you've been a great help, i really appreciate it.

GM has had the 9.5 14 bolt for over 30 years but has used it very sparingly in 1/2 ton truck over the rears (some Z71's had it because it gave them a better/stronger posi too. I read about the upgrade on some models (long overdue) because of rear end failure when towing heavy loads in the foim of shorter life span and the 10 bolt housing itslef is not very strong either. Never been around a Tundra much but I have owned two Toyota cars and they both went past 200K miles with ease andone still had orignail starter and altenator too. I am not sure what you plan to do with your truck but comapring a Toyota truck quality and smoothness wise to a GM 1/2 is like comparing a cheap Timex watch to a fine swiss movement (the swiss one being the Yota) Toyota makes some of the finest vehicle motors even built and that V8 in Tundra is a jewel. YOu choice has to fit you though for what it is worth. One more thing, not sure if you are looking for a crew cab truck but GM makes a 1500HD (not to be confussed with 1500LD CC) that only comes with a 6.0 and is really a 3/4 ton truck with a 1/2 ton label and uses the same tranny and engine as a 2500HD and same tire size/cap too. The LD 1500 CC has a 5.3 and a lighter duty 4L60 tranny while the 1500HD has the proven 4L80 which is based on the old legendary THM400  I have one (a 4L80) in a 2000 K3500 that is starting its 8th season pushing snow (got it in Nov 99)and it has been a good tranny

Well i plan to use it for almost everything. I snowboard in the winter, tow a ski boat in the summer and haul stuff through out the year. so i need it to do everything. but like i said, i like my stuff to be overbuilt so i know i can depend on it in the most extreme circumstances just in case. I suppose i will just have to test drive them and see witch one works out best for me.