So is it possible to get over 10mpg with a 460, HD extended cab 4X4 with the 3 speed? I replaced my fan clutch as it sounded like a jet taking off and I figured that was hurting my mpg a little, but even tho it is quieter it still gets 10mpg. 1989 model with 32,000 miles. would putting a cat back exhaust really do anything other than make it sounds better? It is stock exhaust and air box, stock 16 inch 235's etc. My buddy said to put syn. gear lube in the rear diff. but I can not imagine that would make any difference on such a heavy rig.

 

I had previously owned a GMC with a 454 and got 15mpg so I was thinking it would be at least close, don't expect to get great mpg but was hoping for more than 9-10mpg. Should not need a rebuild as only has 32,000 miles LOL. Just seems like get close to what my hd gmc did.

 

I bet the GM had an OD tranny.

What gearing is in the F250? Do you use it for a lot of heavy hauling? If not and it has 4.10's or something change to 3.27 or there abouts and you'll see a big improvement.

 

3.55 gears. Yes GMC had an od. So short of swapping trannies and gears (both more than I want to spend) no real way to up to 13mpg? free flowing exhaust and air cleaner no real effect on mpg? I bought this from the original owner last year with 29,000 miles and at the time it seemed like a good deal but dang the gas gauge needle moves faster than the rest of the truck LOL.

 

Best I ever got out of my 460 was about 8mpg, and that was running about 45 down the road. So I just went ahead and turned it into a pulling truck.

 

The best bet would be to S***can the C6 and install a ZF 5 speed at least you will benifit from the no slip nature of a manual and the OD. Bottom line, its lotsa weight and the CID of 3 to 5 car engines under the hood!

 

Curious what all would it take to install a 5 speed? probably cost more than the truck is worth as I paid $5000 for the truck but I am guessing it aint worth $3500 today because of the price of gas.