I'm a fan of the Tacoma 2WD trucks. I consistently get better than 25mpg... and I think it'll tow 2000 lbs. I've heard the Dodge Ram turbo diesel 2wd trucks get pretty good mileage too, with much better towing capacity.
The caps, from what I've read on here, make a ~5% difference in mileage vs an open bed w/ the tailgate up.
__________________
|