The best way to increase your fuel mileage is to lie about it. That's what my Brother-In-Law does with his 08 Furd Super Duty with a 6. 4 PowerJoke.
:-laf Seems to be a common solution. . I love the recent report of the guy that pulls 2 trailers and is getting something like 18.
1. Well inflated tires with not too aggressive treads.
2. Try to keep EGT's at 600 or lower, or at least as low as possible.
3. Remove things that cause wind drag.
4. Some people claim bed covers help.
5. Keep the tailgate on, on our trucks.
6. Drive slower, less rabbit take-offs.
7. Use thinner oil - I'll stick with 15/40 though.
8. Lock up switch on auto trannies.
9. Use the overhead readout instead of actually calculating your mileage (usually good for a few mpg's)

10. Lie (as stated by Grizzly)
11. Get a 4x2 single rear wheel truck.
12. Less A/C use.
13. Time the lights to where youre not stopping and starting as much.
14. Drive downhill - both ways preferred (with the wind).
15. For 2nd gens - Keep the IAT clean.
16. Avoid using the exhaust brake when possible.
17. Make passengers use their own cars.
18. Use the coolest air possible - upgrade intercooler - intake horn.
19. Dont gas it before the turbo is spooled - smoke=wasted fuel.
20. Increase timing - moderately.
21. Decrease off idle fueling.
22. Drafting. (Ferds & Chevy's preferred)
23. Dump any extra weight (run with less fuel in tank), leave spare tire at home - haha.
24. Wax your truck a lot.
25. Dump the fueling boxes.
26. Get a second job to pay for fuel.
Hopefully those were very helpful.
