The tail gate and bed cover work... Problem with myth busters is that the drag doesn't start to take effect until after 65mph.. Aero sensitive things really don't work till after 70mph, wings, spoiler, splitters and dams don't show there muscle till after 70, usually 80 mph and up.
To show this is true whenever you want to check drag or a aero mod tape pieces of 1.5" or 1.25" string in that area about 3" apart in every direction...take a drive and watch it, make your aero change and do it again...
For a bed, take a wiffle ball, or a closed wiffle ball or plastic cup...place it in the bed and watch it at different speeds... you'll notice the air comes over the cab nose dives into the rear gate and then comes forward to the cab and back again... Watch as the speed increases... Then watch mythbusters again... notice they never got to the speeds people travel in the real world