You are gonna burn what you are gonna burn. Like most I have some concern about fuel economy. I try to drive at a speed that the truck will get into the highest gear possible for the road conditions.
Having 2 tanks is nice. I can go 700 miles between fillups towing. I can play the best price game using gasbuddy & get through states with higher priced fuel without refueling.
I reset one of the odometers at each fillup & switch tanks at 300 miles. Usually at 1/3full on the second tank we are getting serious about getting a fillup.