Lowering it doesn't sound like a bad idea since I saw an ad of the Eibach Pro-Kit for the new f-150 and it helped Fuel Economy by something like 1.5 mpg. I don't know how much of that is true, but since it sits so high up this might help. Also if/after you lower it, you might want to get rid of those step rails. This might help aerodynamics, since from the picture they look like they stick out a bit.
Also you might want to look into this:
http://ecomodder.com/forum/showthrea...d-cap-583.html
Even though I don't think they are for sale yet.