89 F250hd with 7.5L and C6 auto, 4.11 rear.

Nice truck but the mileage is killing me. It barely makes it to 10.5. Even after complete tune up. I realize the biggest factor is the RPM. At 65mph, I am turning 3,000. I want to reduce that. I am thinking 3.55 or even higher than that. 3.23 maybe?

I do realize my towing performance will worsen with anything higher than stock 4.11 but with the big-block 460, I am not that concerned.

 

You could go 3.08's if you're not towing heavy stuff. 3.23 is probably a good compromise.

 

Spend that $700-$800. It just might get you up to 12mpg. 460 - C6 normal mileage is about 10 mpg rarely someone actually gets 11-12. 460's never have been known for high mileage. My E350 with 460, C6, 3.55 gears will get a maximum of 12 mpg with summer gas and ideal driving conditions. People who tell you they get 14-15mpg or better with a 460 don't know how to calculate their mileage or they lie a lot.

 

Dont' feel bad dude, couple of weeks ago, my 1992 300 I-6, C-6, 3.08 gears-Bronco did 9MPG driving up/down hill fully loaded. For a 460 I believe if you do mostly HWY driving an O/D tranny would be best and maybe going to 3.08 but not any higher, you have plenty of power w/ the 460 and towing might not be much affected. My truck does great hauling with stock equipment, yet the mileage part I don't like too much, thinking maybe an OD tranny yet the C-6 is supposed to be the best tranny ever... Good luck

 

Well, actually I live at 8.000ft above sea level and that worsens fuel economy, especially since I don't have EFI in my rig.

 

i am with rclarke on this one. the cost of putting the higher gears in the truck will not offset the higher prices at the pump. and im afraid that you just may be disappointed aswell with the little amount of differance it will make for your fuel mieage. you did not mention if this is a 4wd or a 2wd truck. if it is a 2wd truck, you would be better off finding a rear end complete with the gears that you desire then to swap out ring and pinion. at least then youd have a rear end worth somethin to someone and you may be able to recoupe most of your money for the swap. good luck.