From what I've heard on this site, a grill block is most beneficial on the uppermost portion to direct the airflow up and over the truck.
Other mods of note:
Front wheel arch gap filler
Rear wheel skirts (huge on a truck!)
Moon caps for a mpg or two
Low Rolling Resistant tires
A boat tail off the back, maybe removable for use on longer drives
I've been working on my truck and put in an aerobed, partial grill block, partial belly pan, and wheel skirts, and my EPA was 25 mpg, but I'm averaging 35.5. Over 40 on the HWY. My current project is a boat tail on hinges off the aerobed, extending 5 feet beyond the bumper.
Again, this site has informed me that 10-12 degrees are the ideal angles.
I can't wait to run into somebody else with an aerobed sometime. Seems like it's picking up steam.
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