Tailgate attached partial bed cover.
 

https://www.youtube.com/watch?v=MT-eTZjzrgo

https://youtu.be/MT-eTZjzrgo

This flip up partial bed cover is interesting. This video is the first time I have seen it. I would like to build one.

Interesting bit starts at 3:15

It's a top-hinged flap attached to the inside of the tailgate that opens upward and makes a flat surface on about the last 1/4 of the bed length.

Magna says it's more aerodynamic than a full tonneau.

Similar claim as GM's partial tonneau - but with much less "tonneau" area.

It would be interesting to see if there is a difference between a partial and a full bed cover by testing. I could do it once I build a partial.

tonneau length and Cd
 

As early as 1981,Ford knew that 12-inches of plywood,spanning their pickups bed rails,ahead of the tailgate would show at the gas pump.
In 1986,GM's drag table for their C-10 pickup indicated a drag minimum right at 50% coverage (rear-to-front).
The TESLA claim may be valid only for this specific vehicle.

It's a component supplier called Magna. They're developing 3 "active" things aimed at the pickup truck market; grill flaps, front spoiler that deploys at speed, and a flap that attaches to the top of the tailgate inside the bed and flips upwards.

Had to dig up this old classic:

http://ecomodder.com/blog/wp-content...ckupAero1.jpeg

Now if they could combine it with a wing.