Towing will use gas. That's just the way it is. Most any gas V8 truck towing the average RV trailer is going to be in the single digits with fuel mileage.
As for towing with a manual, automatics have come a long long way in the last 10 or 15 years if you get one in a truck designed for towing. 6 speeds is the minimum with some having 8. Most all of them have a T/H mode that can downshift for you when slowing to aid in engine braking. Most all of them have a manual mode if you really want to shift for yourself.
But, you are correct, if you want a manual in a truck it's got to be a Dodge.
