I found this PDF-link to study of "DRAG REDUCTION OF PICKUP TRUCK USING ADD-ON DEVICES"...

http://csus-dspace.calstate.edu/xmlui/bitstream/handle/10211.9/169/combined-finished.pdf?sequence=1


And here's a guy mounting and testing all kinds of spoilers and airdams on his Chevy Truck...
(I dig the MacGyver-factor of his front airdam-solution though.)

Front Airdam from Garden edging.
http://forums.pelicanparts.com/off-topic...-effective.html

Tailgate spoiler
http://forums.pelicanparts.com/off-topic...experiment.html

Cab roof spoiler
http://ecomodder.com/forum/showthread.php/roof-spoiler-pick-up-truck-cab-phase-1-a-19525.html