well the tricks i have learned to safe fuel are:
- well keep the total weight down, so keep your truck as emty as possible. Toss the junk.
- don't stick and flags and stuff on the outside. It adds drag.
- change gears in time (well if you have a stickshift).
- Keep your tires on the right pressure. low pressure means more drag.
- keep your car well maintained and well oiled.

No idea what the airfilter will do to safe fuel. But having a clean filter will let the enige "breath" more easily.

Ofcorse not driving the most fuel economical methode.

hmm... i just converted the cost of regular unleaded gasoline in the netherlands, to gallons and dollars. It's 9,86 dollars a gallon now.