http://ecomodder.com/forum/showthrea...d-cap-583.html
Off the front page. This mod actually pays off since pickups use so much gas to start.
The only other aero mod I can think off is factory spoilers, some (not all) I'd think would help reattach air flow on some sedans. This would have to be tested to know for sure, but some spoilers would be pretty cheap at the wrecker.
Ian