Fuel Mileage
 

I am installing an aftermarket computer program, they suggest removing the Onstar fuse, do you know which one it is?

#2 and most important, I have a 2008 GMC 1500 with the 6.0 and 3.73 gears. Killing me on fuel mileage. Any suggestions would be appreciated.

What do you think about a change to 3.42 gears, I am getting about 13mpg around town and 17 HWY...please help.

Thanks for all your help.

Richard

RE: Fuel Mileage
 

i just traded my 06 5.3 with 3.42's for an 06 VortecMax 6.0 with 4.10's. not sure on its MPG yet but with the 5.3 and 3.42, intake, exhaust, and custom tune mostly got 14.5-15 mpg so not great (90% city). 3.42 will suck around town and and for towing. for the cost of changing gears (1200+ for a 4x4 to have someone do it) it will take a very long time to recoup that in gas mileage. the best thing you can do is intake, custom tune, exhaust, changing over to synthetic oils, and keep your right foot out of it.
i tried to drive my 5.3 one time as easy as i could, i mean easy. never getting above 1800-2000rpms. not using air (95deg outside), cruise control everywhere i could,everything you could think of and i squeezed 15.9mpg out of her but it just wasnt worth it.
the 06 6.0 i have i can already tell she is going to be in the 10's for winter and lucky to get 12-12.5 in the summer. so i can feel your pain.
as for the onstar fuse, im not really sure. i think it might say on the fuse panel covers but not sure.

good luck. let us know what you do.

RE: Fuel Mileage
 

I've switched from 410s to 342s, and my personal experience is if mileage and highway driving is what you want, they're good. They drop about 700RPM off your top gear at highway speeds, so far I calculate my highway mileage improvement is 3.5 MPG. Hope you've got a GPS unit to give you accurate highway speed till you adjust your PCM.Rule of thumb is under forty, you're doing about 5MPH faster than the speedometer says, over 45 you're going 8-12 MPH faster. Down side is you lose low end torque and power, so if you want power, Tow a lot, or go offroad with big tires, these may not be the gears for you. 04 2500HD,4X4-6.0L-Eng-4L80E-Trans-Stock-E rated 16" Tires.
Around town, I measure fillups by time intervals. Usded to be 7-8 days between fill-ups, now it's every two weeks or more, so in-town or city mileage has nearly doubled.

RE: Fuel Mileage
 

Yep i have an 06 2500hd 6.0 4:10s was getting 10.8 in town and 12 on hwy now with superchip (performance program) And k&n cold air with dual exhaustim getting 15.3 on hwy and 12.5 in town!