[TimT]

If you really want to boost the mpg's, remove the rear tailgate. Look at it like a giant parachute catching air and slowing you down as you drive.

Urban Legend... MPG does not vary much whether the tailgate is up or down.

http://www.gminsidenews.com/forums/f22/leave-tailgate-up-better-gas-mileage-11678/

"Putting the tailgate in the down position tends to increase turbulence and drag of the open box," explained Jack Williams, of Ford Aero Systems Engineering. "We've seen drag increase as much as .5 to 1 percent. Flow-through, web-like fabric replacement tailgates tend to increase drag even more; we've seen increases as much as 4 to 5 percent." In a nutshell, all of that extra drag translates into worse fuel economy for the vehicle.

http://www.roadandtrack.com/article.asp?section_id=18&article_id=1455&page_number=1