there are so many variables when towing, case in point:
we went from a v6 Dakota towing 5000 lb to a ram 1500 hemi towing 7000 lbs. same 8500 km trip a year apart
trailers very similar shape, just your typical slightly sloped front, otherwise a big box on wheels. new trailer is 6 inches wider, 6 inches taller and 2 feet longer plus 2000 lb heavier
new combo used around 20% LESS fuel even though we were actually able to drive at 110kph on the freeway versus 100 with the v6(it struggled)
biggest difference in my mind was the v8 being lazy versus a hard working little v6.
of course technology came a long way in the 8 year difference between the trucks, hemi 8 speed vs the v6 4 speed