I pull a similar trailer from Ohio to Michigan and Montana/Idaho with my 2018 GMC 2500HD diesel and at those speeds, I’m averaging 10-12.5mpg. It’s the wind resistance much more than the weight.

It's something with wind resistance/physics, but if you go beyond 65 mph the MPG begins to quickly drop off a cliff. I've got the 7.3 with 4.33 gears and It'll get 10.5-12 mpg pulling a 6-8k horse trailer.

In aviation anything moving through a air mass creates parasite drag. I drive this truck at 60mph and get 18-20 mpg. Anything faster or a head wind would disrupted the even(laminar) flow of air to cause a disruption of flow called turbulent flow. Like anything falling to the ground will accelerate until it reaches its terminal velocity, at that point it will stay the same speed. With out air if you drop a feather and a steel ball at the same time from the same height they will hit bottom at the same time. My 22 xlt 7.3l 3.44 gears is tough vto turn, is yours?

I see all the nice toys you have and am a bit envious of your success. If you don’t mind me asking, what business or line of work do you do?

Try it again going 65-70

I have the 4.30 I'll give up gas mileage for towing power.

I have a 22 F350 XLT FX4 crew cab long bed powerstroke I’m curious what made you go with the gasser?