which of these three would be the best for my s-10 truck?

[shok]

ok bed cover wins!
i have a 220 mile round trip 5 days a week so it will be easy to chart any improvement this offers.
since the covers are easy to remove it won't hurt the usability of the truck.
I do have a partial grillblock using black gorilla tape which did seem to help, I actually did that almost a year ago and its holding up fine and isn't noticeable.
as for underbody aero mods, I already have that in mind, its just these top three things were at the front of my mind as far as the next experiment. I also have a 2000 gmx jimmy 4x4 which has some underbody pans that have inspired me a bit. They call it a skidplate but its made of plastic
I'll probably just build my own bedcover, i think I can do that in a price effective way.