Im buying a truck soon. 2001 or newer fullsize chevy or gmc 1500HD or 2500HD with the 6.0l, 4x4, ext cab or 4door, automatic. That is if i dont find a duramax with the same options without a ton of miles. As soon as i get it im ordering a 6-8" suspension lift and 35" tires. What gas mileage are these trucks getting factory and about what will the gas mileage be with the 35" tires. Thanks

 

probably around the 15mpg range stock if driven easy. with the lift and tires i would say low teens.

 

How much can be gained from tuning?

 

TTT...specify if you are talking about gas motor or diesel

 

My 03 1500HD, CCSB, 2wd with the 6.0 averaged 11-12 city, no idea on highway, with 3.73 gears on a 265/75 16r all-terrain tire. That's with a CAI, FloPro exhaust, 05 e-fans, and a Wait4Me tune. I don't know anyone getting anywhere near 15mpg with that drivetrain.

 

my 2500HD 6.0, with cranked tb's and 33's with 4.10 gears got an awesome 10.5 mpg city, and 14 hwy.

 

I would guess that you are going to get less than 10 with a gas motor unless you re-gear it to 4.56's. You need to be in the stock rpm range. That said you are still going to get worse gas mileage because of the added weight and aerodynamics being changed by being higher off the ground and wider tires.

 

My 2005 2500HD excab gets about 10-11mpg city and about 13 on the highway . I've got 31.75 tires and a level lift. Stock I got about 13mpg city.

 

i get about 10 in the city and about 14-15 on the highway. then again i do tend to have a heavy foot. thats with a 6.0, 4.56's, 35's.....