[brucepick]

Welcome to EcoModder. Getting max mpg out of the truck you need to drive sounds great!

If you didn't see them already, go have a look at the two stickies at the top of the "EcoModding Central" subforum here. And there's a similar sticky or two at the top of the Aerodynamics subforum.

My favorite biggies that can really help, without changing the look (or not changing it much) are:
Higher tire pressure. Just remember to reset it after the dealer lowers it during service visits!
Grill block (use your soon-to-be-bought ScanGauge to monitor engine temp digitally)
Tapered cargo cap would be super on the pickup.
Warm air intake? Apparently it helps some designs more than others. If you try it, use ScanGauge to monitor the intake air temp.

Underbody smoothing panels. There was a thread somewhere, a guy with an off-roading Subaru who put metal sheathing underneath that was aero and also protective. Watch out what kind of fasteners you use. Dissimilar metals will corrode. You can look it up in Wikipedia for good details. Rubber "well nuts" aka expansion nuts could be the thing. Or you could strap around the framing so you don't have to drill into it at all. Might help protect your warranty. Am I still making sense? I'm up way past my bedtime.