[kach22i]

UPDATE:

I did some test driving today, some observations below.

45 mph:
You can really feel the aero down force, I'd say there is just as much at 45 as there was at 50 mph before.

70 mph:
The truck tracks really good, better than before - likes to stay in a straight line (which is good).

80 mph:
More down force than before, just shy of that feeling that you are towing something, feels very secure for a vehicle which sits so high off the ground.

There is still some buffeting and deflection of the material past the last spar - just before the rear spoiler. However it is 1/8th to 1/4th of what it used to be. I can see that a perfectly rigid top for the bed would be an even greater improvement.

I was seven pounds low in tire air pressure, huge improvement in rolling resistance now.

I was so happy with the results, that I went to the self-serve car wash and gave her a bath.