I have a 1994 F150 with the 300-6 and an E40D and I am averaging 11.5 for overall driving. For me thats about 80% in town and 20% highway. I got 11.4 when I started then I changed Plugs Cap and Rotor and seemed to get about 11.75 mpg. Both of these numbers are a minimum of 2 tanks of gas each. I did the 6litre tuneup and was checking it when I borrowed my buddies diesel to go to Utah and get my 5th wheel and while I was gone he filled my truck up. So those numbers will be skewed for a tank or two.

 

Our trucks are similar. Iv got a 1992 F250, 4wd, 460, E4OD, but iv got 3.55s and I get 10-11 period. Doesnt matter if I drive like a grandma, hot rod it, or tow a 6000 lb racecar, it gets about 10.5. Mines got true duals, and replaced the intake box with 2 open elements. That might have helped but not much lol.

 

My 89 f350 with Holley carb and intake with lt headers gets 11 on the highway with the t19. That's with a 15' flat bed and 4.10 gears at 55 keeping out of the secondaries.

My 06 f250 with the 6.0l diesel can pull that with 10k pounds behind it set at 70 with 4x4 an auto, exhaust and a 3.73 rear.