also, more ideas:
- swap gears / final drive ratio to a lower numeric set
- run 'fuel max' or other 'ECO' tires
- run narrower tires
- lower truck
- tonneau cover
- remove unnecessary weight (junk in trunk)
- drive slower, drive smoothly, coast into stops, etc. (braking = lost energy = lower FE)
- use A/C (and defrost) as little as possible
- use cruise control as much as possible (except in hilly terrain where it will downshift too much)
- high mileage truck = fresh (front) oxygen sensor(s?); as they age, they read lower = more fuel