Got my adjustable trailer hitch yesterday...just over $90 shipped.
I ended up tucking the Gurney flap so it's not active. I can easily flip it back over when I want to.
Two trips up and back without a trailer has been netting me between 23.5/25.1 from Houston to College Station and between 26.5/24.2 coming back. Standard tool and overnight bag loads in the bed.
I probably won't have the chance to scale it with the trailer so it will basically be off the cuff on estimations.
I did notice that when I had the hatch up to divert the air over the trailer, the airflow was pulling stuff into the bed. I actually saw a sheet of paper in the road and ran over it. It ended up flowing under the truck and into the bed. It was someone's shipping receipt. I might end up lowering the extended rear diffuser a little lower so the air flows under the trailer more instead up into it.
I do make it a point to carefully inspect the trailers on site and before I git on the road. I've read many stories about how many U-haul trailers fail and I don't plan nor want to be part of that statistic.
I might be tempted to throw the fiberglass camper top on fer just one run up and back with a trailer and see what I git. Depends on how much time I'll have to make that attempt. It's been a long time since I've had it on the truck...