[brucepick]

Looks like you have an excellent start. Already getting nearly 32% above the EPA combined number, and you just got started.

Rear wheel skirts look like a likely possibility. I plan to make mine go down just till they come close to the tire, not extending into lower part of the opening. That way I won't be bulging the lower skirt out to clear the tire. If you also do flat wheel covers the combination should help you.

I read that a one foot wide board across the back of the bed, by the tailgate, is just about a definite mpg improvement for a pickup. I won't drag you through the aerodynamics theory (OMG - very bad pun!!) - sooner or later you can start reading in the Aerodynamics subforum and you can learn all about it. But planting a board or two across the back of the bed should be pretty easy. If it doesn't help, just take 'em out again.