It can't be that much worse than the aero of the 88 F150 4x4 one of my Guard buddies had; it was powered by a very healthy 302 (199 dyno'd whp) and it got 27-29 mpg between fillups throughout the 4 years I knew firsthand (when I borrowed it to move) and secondhand (the owner's account) of its operation. Of course, all that is with the drivetrain in the 2WD configuration, but still ....