True-But I can tell you my 5.3 in my Silverado will pull my 5,000 foot trailer up 8,000 foot passes (on a regular basis BTW-based on where I live) in the summer with no issues. Yes-it revs like crazy in lower gears but is built to do so. I pull at 65mph on a level highway at 2,000 rpm to get 12mpg. Anything more than that speed and gas mpg further declines. Based on what I have read the Ford 3.5 doesn't do much better under the same level highway situation.
https://www.f150ecoboost.net/threads/towing-fuel-economy.18049/
They all all return "about" the same on the straight level pull with the same load because it take X amount of energy to sustain say 250 LB FT.
I wouldnt expect any gas truck to significantly do better than another providing they are all geared " about" the same.
If Im towing and I need the performance like an uphill 2 lane pass - I'm ready to sacrifice the MPG for that performance.
Its going to take more fuel to give you 479 Lb Ft than it will 410, and at that moment I'm ready to spend it so
The ford and toyota will always be able to consume more if you ask them too.
The turbo trucks give you this where the NA trucks are simply out of wind.