[elhigh]

Your add-on needs a less-sharp angle to it. Ideally you want it to progress in a gentle curve from the end of the cap, and the sharpest it can angle down is 15 degrees from horizontal. There's lots of discussion about taper angles for fairings and whatnot under Aerodynamics. I warn you, don't start reading if you have to be somewhere soon.

Yours looks taller than the standard Yota 4x4. Is there an aftermarket lift under there? If you don't do any offroading, you could go in and remove the lift kit and bring it down to stock ride height.

The wheelwells are an awful lot of open space; the rear ones in particular don't have much wheel in them. Even if you don't bring the truck down any, closing those off with wheel skirts will get a couple of big air buckets out of the picture. You could also close off that portion of the front wells that never has wheels in it, if you don't do any offroading. If you're a rockcrawler, though, leave them open or you may wind up stuffing the tires into the skirts. That just screams "amateur setup."

Move the spare into the bed and you can make a belly pan that covers everything astern of the rear axle - that's an easy start. I haven't done any on mine yet, but that's probably where I'll start when I do start.

I'm hypermiling my truck with the 22R engine and getting great results - up to 37mpg so far. You've got the disadvantage of the 4x4, but since all I've done so far is change my driving habits, I bet you're in for one heckuva shock when you change yours.

Hey, start a garage entry for your truck. Go to the top of the page and click on "EM Garage."