JakeBrakeIH

iTrader: (22)

with that kind of gas mileage, there has to be something wrong...when the last time you did a full tune up? as every one said a custom tune will help but you should be ATLEAST getting 10-12MPG at the worst now...lol Ive heard of people getting better mileage pulling a trailer loaded with 8k on it

TX Tahoe Z71

iTrader: (28)

With that many miles, you need to change the plugs, wires, fuel filter, air filter and add a big bottle of Techron injector cleaner when the tank is pretty low. Seafoaming the top end, cleaning the tb and MAF are probably good ideas as well. There is a good writeup on Seafoaming on LS1Tech, I believe. Then after all of that, get a good tune.

But as was said earlier, 6.4 mpg is way too low, something is not right. I would start with the cheapest fixes first, like plugs, fuel filter, injector cleaner, etc. to see if it starts improving. Best of luck and keep us posted!

KLUG'S SS

iTrader: (6)

Seriously though, our 2001 Chevy 2wd at work with a trailer hooked up to it all the time at least pulling 2k-4k in weight gets no worse than 11-12. I would definately say their is something wrong.

Dark Halo

iTrader: (14)

to answser all my truck has fastory 20's but they did not come on the truck new. The truck has 66000 miles on it and the tires are 275 60 r 20. I am getting about 12-14mpg

joeyc125

iTrader: (7)

ha 6.4, our 8.1 avalanche we use at work to haul bikes get 8.8 with a 28' 12k pound trailer! check her over good, definitely not healthy. But i hear you on the winter gas here in mn, i lose 2-3 mpg during the winter in all my vehicles