So i just purchased a 2010 Yukon Xl that has a 6 inch lift and 35x12.5 wheels and tires all the way around. I know the transmission and torque converter and completely cooked. My question i keep being told by a couple shops is to go with a stage 2 transmission. But i was also told to go with an oem or stage one and change the rear gear ratio as it would make it much easier on the transmission with changing the gear ratio and would allow for better mpg in the long run. I don't know a lot about transmissions so i figured this would be the best place to get information/figure out which parts or gear ratio to go with. Thank you for reading and any help is greatly appreciated.
The term "stage 2 transmission" is meaningless. Have them spell it out EXACTLY what that entails and put it in writing.
When your truck had stock size tires on it, she was cruising at about 1,575 rpms at 70 mph. Now, with the 35s, she's cruising at about 1,422 rpms at 70 mph!
In stock trim, these trucks run great with 3.42 gears and turn about 1,749 rpms at 70 mph. That's your standard, not 1,575 @ 70.
So, having said that, 4.10 gears will have the engine turning 1,895 rpms at 70 mph. That like 3.73 gears on stock tires. A little more oompf off the line.
4.56 gears will have you turning 2,106 rpms at 70 mph. Once the engine and transmission are tuned for that gear, there's a good chance she'll smoke the tires off the line with 4.56s.
I have a truck with a 6.5" lift on 35s with factory 3.73s which are like running 3.42s. I mean to change it to 4.10s but it's not been a priority after 13 years!
In order to change gears in your current carrier, you'll need an adapter. I know people that have used them without issue, or they never fessed up. I believe the better option is to change to the larger carrier that runs 3.42 gears and lower (higher numerically) since you are running those heavy 35s.
If yours were mine, I'd ditch that little 8.6" axle and use the 9.5" 14-Bolt axle from a RWD Denali or Escalade with the "AXN" RPO Code. I did this with my Yukon XL a few years and swapped from 3.42 gears to 3.73s. They can often be purchased for about $200-300 from LKQ salvage yards and most don't need much more than new seals and the gear swap. Mine was zero timed.
Every pound of reciprocating weight you add to the tire/wheel assembly is like adding 8.4 pounds to your payload. For example, your 35s may weigh 30 pounds more than the stock setup and that's like adding almost 1,000 to your payload. My pickups at the track with their stock 6.2s put down 375 rear wheel horsepower through the traps in the quarter mile. With the heavier tires they lost 50 horsepower (325 RWHP)! Now image the kind of power lost to your 5.3 at the wheels because of all that weight. As my daughter used to say, "smiles per gallon, Dad!" Yeah, I was paying for her fuel back then! LOL
Stock Size Tires and Current Gears Example:
35s and 4.10 gears Example:
