ramair383ci

Ok I put 4.56 gears on my 1500 gmc 5.3 which has a 6" lift kit and 36x15.5xr20 MTZ's. I was getting 11.2 mpg's with the 3.73 and that set up, then I changed to 4.56 and I was expecting to get better mpg. Oh I forgot to mention that I have a tune also. Well it now gives me 12.3 on a 3 hours tip which I was going at 75-80mph. My rpms are at 2300 at 75mph and 2500 at 80mph. I heard on this forum that people with 35's with these gears would get almost stock mpg. I'm just wondering if i'm getting very low mpg because I have such a heavy tire. Please shead some light on me.

IMD

iTrader: (10)

sounds normal to me. not sure why youd expect to get stock gas mileage with hug tires, a huge lift and big heavy wheels.

2002C5COUPE

iTrader: (3)

the epa mileage rating is not based on these trucks traveling at 75-80 mph. try slowing down and your mpg will improve more

skyhighsami

iTrader: (8)

For gods sake Hug your tires they need it.

Tootall

iTrader: (79)

did you get retuned for the bigger tires? what pressure are you running.

The heavy lugs make a huge difference.

ramair383ci

I believe they are at 45psi which they are wearing out evenly.

nonecktribe

the gears alone will prevent you from seeing good mpg...thats why chevy went to 3.23's and 3.42's for the rearend gear ratio instead of 3.73's...they were trying to up there posted mpg...

chevbowtie22

I'm running the same tires and I can squeeze out 12 mpg on average with my 4.88's. Try slowing down on the highway a little and see if that helps. The weight of those tires is whats killing you. When I switch over to my 315 75 R16 DC FCII's in the winter I can get around 14.5 to 15 mpg per tank. Your only real option is to switch out the tires.

quicksilverado

iTrader: (8)

The 4.56 gears will help him with tires that big.