I have a 2007 Silverado Z71 crew cab. The truck was bought from the
factory as a Rocky Ridge Conversions(6" suspension lift, 35" tires, 20"
wheels and a few other things). I'm getting about 12 MPG and I am
wanting better MPG, I do a lot of highway driving. I am wanting to
regear but need to know which way to go.... I think currently I am
running 4.10's. What do I need to go up to??? Is there anything on the
negative side I need to know about???

If I do it will it void my warranty? I have a 5-year/75,000 mile bumper
to bumper warranty. The truck only has 6,000 miles.

What do you guys think?

 

3.73 or 3.42 gears will give you better highway mileage, but you'll lose some low end power. I'm not sure about the warranty issue but you would need to recalibrate the electronics.

 

i have the same setup in my truck and i get 17 and i run 4:56 gears in my truck, i think the prom chip helps a little bit though. I blew my rearend up running 3:73 with 6 inch lift and 35 inch tires. Ive heard its rough on your rear end to run that gear ratio with 35's