[elhigh]

For your commute, diet. Pare out every ounce you can. If you don't usually carry passengers and it isn't too big a hassle, removing seats may help you.

For your longer trips (5,000 miles? Seriously? Dang) you could consider fabbing up a sort of trailer tail to improve your vehicle's wake. It won't help you on your daily drives but at extended cruising speeds the savings would rack up pretty fast. If you don't pull a trailer on your long trips but have a hitch, you could make the trail on a frame that installed on the hitch receiver.

All blue sky ideas that are easy to talk about from my comfortable chair in front of the computer.