I got 2004 ext cab F250 diesel with off road package not happy with mileage 12000 miles on truck only getting 15 mpg on interstate going 80 mph should I do better.
I brought it back to garage and everything checked out ok. Am I pushing this truck to hard? Or should I back off to 70 mph. Just wondering what everybody else is getting.

 

I noticed that with mine, same truck as yours, I loose 1 mpg for every 10 mph that I go over 50(according to the overhead console meter). I did, however, gain 4 to 5 mpg by adding a Mac Products cold air intake, Banks Six Gun tuner and a Banks monster exhaust.
The performance was awesome and just today I out ran a 5.0 mustang in a 1/4 mile. To answer your question though, 15 mpg is pretty good for that truck at that milage. It should get better with time.

 

Shoot it hasn't hardly startedto get broke in yet

 

And the dealer wanted to know why I wanted 3.55 limited slip rear instead of the too low but if you buy this truck we won't give you a choice so you get 4.10's! Someday I might slowdown to under 80, but why? Got places to be asap. Ever be 800 miles from home and by the time the racing is done you have 12 hours to be at work? Made it. Barely. But that was an aceptible reason to not be getting fuel milage. Gooseneck trailer with car did hold it back though. The rest of the time is simply too low of gears.

 

I have the same modle and I have 32,000 mi and at best, 75-80 interstate 17.5 miles haven't got it again

 

2003 F-250 with 42000 and I get 13-15mpg at 80mph and 15-17 at 70mph and 17-20 at 55-65mph. I'm happy with them numbers, because with trailer in-tow they don't change to much.

 

I have a 2004 crew cab and i am not getting about 14.3 and have 40k plus and wounder what I Could do to get better.