Pickup caps and wind resistence.

I have used both ways, with a cap for years and other years with out the cap. No difference at all but I like the cap as I can store "stuff" out of sight, locked up. Plus I keep my EU3000 Honda in the bed and do not have to take it out
when I run it

It might have a very slight difference but not even close enough to justify buying one for that reason alone. We got ours to gain covered storage space.

As stated there are a lot of reasons to have a cap, but spending $1,500 to save $100 on fuel is the least of them. I have mine outfitted for a night or two of camping. Not towing the trailer really saves some gasoline.

Wind tunnel tests show the air flying over the bed anyway so a cap doesn't help.

On the other hand, there is one very useful place for a pickup truck bed cap: One can run their generator in one that is well ventilated (the side windows open or at least have openable vents) and it is out of sight/out of mind for thieves.

I don't think you would notice mch difference by adding a cab high cap,instead of the cover you have now. It would add a little more weight, that would nearly offset the extra wind deflection.

I have noticed that I rarely drive straight into a head wind. It seems to always be from the front/side, which catches the TV front, plus most of the trailer front.

I pull a 7-23 enclosed trailer, with a v-nose in the winter. It handles the wind quite well!

Jerry

You will gets lots of opinions... including mine. Yes a shell will improve air flow and to a small degree mileage. The best reason to have one is the secure storage it provides. Drove F-150 S Cab's (2), for 15 years both with a shell. Unless you are going go the fiver route no reason not to have one. If you decide to add a wind deflector, and yes they work, having the shell enables you to mount it closer to the TT which dramatically improves its performance. We got an additional 1.5 to 2 mpg averaging 12.5 at 60. :C