X-2
I towed with a Tundra that I had the Gross Vehicle TV & TT loaded at the maximum suggested weight. Towing on the flat, no problem vehicle would hold fifth gear and cycle to fourth as needed. When I hit the hills I was in fourth and cycling between fourth and third for the most part.
The worst thing was the mileage --low sevens--. I traded and went to the vehicle in my sig and averaged 12.3 on a tow from Harlingen, TX to WV. The Diesel shifted in to fourth on a hill one time. I usually tow at 55 to 65 MPH dependent on traffic conditions.
IMHO more truck is the best choice. Stay near the 50% area if possible and no higher than 75%.