[aerohead]

On the T-100, with the slider open, I get a healthy jet of air into the cabin from the bed. A summer strategy, since the magnetic clutch on the AC compressor went south.
Also, Fem bot S's 1993 Toyota pickup, 2WD, averaged mid 26-mpg @ 65 mph, without AC.
With a cab-high, aluminum bedcover, 30.6-mpg.
She has the 5-speed manual. Wider than OEM tires.
I believe that Toyota rated these 2WD trucks at Cd 0.44.
Finally, in a road test of the Cd 0.37, 2WD, 2014 Tundra:
* with closed gate, at 65-mph, 20.8 mpg.
* with open gate, 21.0-mpg. One example where an open gate produced lower drag ( no data on rear lift ).