The aero cap is probably where you'll get your biggest efficiency bang for the buck if you spend a lot of time at 55 mph. I'd consider starting there.
Or...
I think the tapered bed and the chopped top probably helped. But my gut says the front taper that exposed the front wheels is worse than stock in that area.
From:
http://ecomodder.com/forum/showthrea...tml#post455297