Ram owners. What gear while towing on highway?

In my 2012 Ram 2500 Mega Cab with the 5.7 we would just throw tow/haul mode on and off we went.
Trailer was 11K and I don't go over 65mph.
Always held the gears nicely and very rarely down shifted.
I do not use cruise control.
Our mileage was between 10-12mpg with that trailer.
Should mention we also had the bullydog system installed along with a cold air intake and a flowmaster exhaust.