QUICK QUESTION?

I JUST LIFTED MY '06 CHEVY 4X4 6IN, BUT I NOTICED THAT WHEN I AM ON THE HIGHWAY IT TAKES A WHILE TO PICK UP SPEED.  I ALSO NOTICED THAT MY RPM'S STAY A LITTLE HIGH SOMETIMES, THEN DROP BACK DOWN.  IS THERE SOMETHING THAT I CAN DO TO FIX THIS PROBLEM, AND IF THERE IS PLEASE LET ME KNOW.  I ALSO PUT ON 315 75 R17 BFG TIRES.  THE MOTOR IS A 4.8L DUAL FLOWMASTERS AND A K&N FILTER.  I WOULD APPRECIATE THE ADVISE FROM OTHER OFFROADERS.  

Your problem is very simple to fix but many ignore the reason for it. When you raise truck and installed bigger tires you made your effective gear ratio a lot taller so engine has got to work a lot harder to move it down the road. The RPM surges you are seeing are from the tranny hunting gears and converter lock and unlock as it struggles to make headway. Dual exhaust made things worse because to actually take away for lower RPM torque and a K&N is not going to fix it either. The solution? You need to regear the axles in your truck or live with it being a slug and likely having shorter tranny life too. I'll bet MPG is not good either and OD is worthless. Given that your tires are about 35 inches and engine size I would suggest at the very least here 4.88 axle ratios but even this is a bit light with 5.13's being better. Before you panic and think 4.88's are too deep and a 4.10 is all you may ever need, what you need is based on tire size and no one axle ratio does all. With 4.88's at 65 MPH you will only be turning 2100 RPM in OD which is almost marginal for a 4.8 pulling that tire size and drag of lift. Even a 5.13 would only add about 100 RPM to cruise RPM. You are not a lone in your mistake and many lift trucks and never bother to regear them and they blame the truck when tranny or other drive line parts fail early or blame engine and tranny or truck when it does what yours is doing because they seem to never even consider it is because of what they did to the truck that caused the problem. BTW, Your truck can have a GU5 (3.23) GU6 (3.42) or GT4 (3.73) in it. My nickle bet is on it being a 3.23 or 3.42 and with that it really has to be a slug at times and even a 3.73 would not be very much better. Until you get this fixed proper, do not even use OD position on shifter if you value your tranny. One more thing, if tranny goes out forget warranty because they can void it if they want too because of lift and tires UNLESS you regear the truck to make up for the added load on drive train (many never consider this either)  

hey SnoMan,

thanks for the info, where can i go to get this taken care of?  my truck has 3.73 ratio in back.  someone told me that i could put in a HYPERPACK and this would solve my problem.  what do you think? the HYPERPACK is supposed to give me more horsepower and fix my speedometer to my tire size.  should i do this? i really don't want to blow out my trans this is my investment.  i would appreciate the advise.

thanks,

rob4x4  

No tune is going to fix this though many want to believe this. It can fix speedo but not loss of performance by any stretch of the imagination. To do the same speed your engine no only turns at a lower RPM because of big tires but it also has to make a lot more torque doing it and it is exceeding its abilty to do so now. Many want to believe that a air filter or tune or dual exhausts can fix anything but funny thing is is that your engine was well tuned from factory on intake and exhaust and if magic gains where that easy they would come with them given the HP and MPG pressure Detroit is under. his is not the 60 or 70'swhere some old hi compression carbed V8's responded more favorably to this because they were not tuned on the intake and exhaust like they are today. On gears I would suggest you by them online and shop around for best price to get them installed. The dealer is the last place you want to do this unless you want to pay a small fortune to do it. (even then they would not have 4.88 gears) You install some 4.88's and you will think you installed a much bigger motor in your current truck because it will run a LOT better. 4.8 is a good engine (I like it better than 5.3) it just needs to be able to wind up some to make its power.  

I also forgot to add that Yukon is a good brand of gear to get and you should have a 8.25 IFS ring and pinion up front and a 10 bolt GM in rear. Both of those drive axle have been in uses for about 20 years or more (the 8.25 dates to 88 and the 10 bolt to early 70's and gears have not changed.  

thanks for the info, man i would have never guessed lifting my truck would require so much time, effort and money.  don't get me wrong i love my truck and would do anything to preserve its life.  i guess you can say i didn't know what i was getting into.  this is my first 4x4, and of course the first time i lift one.  if you can think of anything to help me more i would greatly appreciate it.  

You are not alone, many lift there trucks and install big tires and wonder WHY performance has suffered. Many skip the gears and then complain about junk trannies when they fail under the added strain. It just never seems to occur to them. One more suggestion, not not use 87 octane, try at least 89 octane for a few tanks and I think you will find that it runs better and is actually cheaper to drive because it will use a bit less fuel. The knock sensor on that engine masks true octane needs by retarding spark before you hear knock. The only problem with that is when you retard spark you hurt performance and MPG. (please note, all Detriot CAFA MPG tests are done with 93 octane but they never bother to tell you that either)  

hey i have a 01 2500hd 4x4 and i have the tortion bars lifted right now but im thinking about lifting it. my buddy has the same truck and he has a 3in body lift and are trucks sit almost dead even and we both have 33in tires under are trucks. what kind of lift should i put on it a body lift or a suspesion lift. im thinking about puting 35 or 36 on it once i get it lifted.
i would appreciate it some one could give me some addvice.  

Randy's stocks the Yukon gears you need... I have priced them out in the past.  

Rancho has a 4 inch kit that will fit 35's. www.cognitomotorsports.com has a bunch of stuff for your rig. You could go with a body lift but it won't give you the articulation of a suspension lift. Here's a link to an article that might give you some more insight:

http://chevy.off-road.com/chevy/article/articleDetail.jsp?id=429856