Yeah .... It is putting down 2x the torque.
The 8.1L was rated at 320 horsepower @ 4800 RPM, 450 ft-lb @ 2800 rpm .... great power band for a towing gas motor .... but, go up to 5,000+ feet and you're probably getting somewhere around 275 horse and 400 ft-lb out of it, which is still enough to tow the loads I was hauling well enough .... but .... even at altitude, the diesel will put down 800 ft-lb because of the turbo .... so yeah, there is that
i had a 5.7L tundra before the 6.7 cummins. i know....apples to oranges.... but i can relate to what you are saying when getting in elevation. i pulled an 27' enclosed, and it had its hands full in the mountains.....