MPG with late model Ram 3500 with 4:10 carrying TC.

Laramie leather is cheap I've heard...vs Limited or longhorn.
Mileage? About the same. 4.10s will hold 6th more, but that makes no difference. 6th is an empty cruising gear, except with deep gears like you're looking at.
Won't help mileage much. Check your mileage in 5th and 7th at say 70 mph flat road. Shouldn't be much differnet.

Regardless of gears, a TC and a light trailer isn't at the upper end of any new diesels capacity. But you're correct, 410s will make it even easier.