Hey guys, I"ve asked this question before but a second opinion couldn't hurt right? I need new gears for an '01 Yukon w/ 35's. Mostly used for a short daily commute, river trips a few times a year(600mi. round trip),and offroading 1-2 times a month. Currently this thing is a slug with low rpm's. I don't know how to figure out the sizing equation cuz I dont know what gears I currently have nor the type of axles.All I know is the front is IFS and the back is a 10 bolt.
4.88's were suggested, what about 4.56's? What would be the difference? I'm looking to not fry my tranny and hopefully gain some mpg's back. a few horses wouldn't hurt either! If I were to order new ring & pinions (YUKON), what are the specs? Thx.  

with the 4:88's and 35" tires @65 the rpm will be about 2150. that's why we figure the 4:88 is the best option for the 35's for power and economy.

the 4:56's will turn 1992 rpm, right where the sbc doesn't have much juice. a small hill will likely cause a downshift. I suppose if you drive 70+ mph and have no intentions of towing the 4:56 would be ok.  

i have a gear question! me and my dad just put a dana 60 front end in our jimmy! but heres the question the rear 14 bolt has 4.11 gears but the 60 has 4.10's, would it be ok to leave the gears alone or do we need to change the back gears to 4.10?  

nope they will be good tyler.  

The only issue here is the the actual effective ratio. If you are tunning 35's or so, a 4.10 is not enough. Some think a 4.10 is the perfect ratio but there is no one ratio fits all as it must match tire size and usage. For stocked sized tire I would say a 4.10 is about perfect for a full sized 4x4 but beyond stock tire sizes it is not. Also a 4.11/4.10 combo is not cause for concern at all. I had a truck once that had a 4.09 in front and 4.10 in rear and came that way. I theory you actually want front axle to bit a fraction taller anyway as 4x4 tend to handle a bit better at times in 4x4 that way because the front axle is always a tiny bit "ahead" of rear axle.  

well, back to the three speed and a 4spd manual again and tyler lives in a 55mph speed limited area,....at 60mph 4:10 gear and 35's will be turning 2350rpm. It may seem slow starting off but it is efficient and effective,.......leading to the 700r4 being a  better choice and the 4:10 to tall.....  

well i think the reason i dont really care is because i have a small car so i dont drive out of town in my 4x4 so if i do go to browns camp or the beach it's 55 all the way dude.  

For many years I drove trucks with 30's and 31 with 4.10's and no OD and a few of them cross country too. Even a 2800 to 3000 RPM cruise is nothing for a SB. I drove a 72 GMC 3/4 ton with a 465 and 4.10 gears from 74 till about 83 and I used to get about 14 to 15 on highway with it and in 13's when I was pushing 80 or a bit more.  

I do tow boats once in a while. A heavy boat, short distances and a lighter one at longer distances. If I were to order new gears, for what type of axle(s) do I get them for? '01 GMC Yukon 5.3L 4x4 6lug.  

Your front axle is a 8.25 IFS and rear axle is a GM 10 bolt. Being this is a Yukon if has a .70 OD and with 35's I would suggest at least a 4.88 since you tow some. This would give you about a 2100 RPM cruise in OD at 65 and about 3000 RPM in 3rd/drive which would put it right at the beginning of its power band and it would tow well even on a hill. Gearing it taller would gain no MPG or lifespan and would render OD less useful too as while 5.3 have good power for their size at higher RPMs they are not known for lower RPM torque.