To add to this, once you’re plugging on down the highway, how much power it takes is less about weight (to a point) and more about wind resistance and speed. Bigger tail will wag the dog more, but won’t affect mileage at a 1:1 ratio based on weight.
I managed to get 9 mpg in my good mileage diesel this weekend for a stretch just pulling a little 6x14 v nose maybe 3klb tops into the wind (at 75+mph). Don’t think I’ve ever gotten that bad of mileage with any of my heavier or larger trailers, including with the camper on.
Reason was, with the 40-50mph head winds, the engine was pushing 120mph of wind resistance.
Regardless of truck I wouldn’t obsess over a few hundred or even a couple thousand lbs.