My brother in law bought a new Tundra to pull his 8k pumper pull a few years ago. Had a 5.7L with the towing package which comes with 4.30 gears. While it would tow that trailer up any hill he wanted it to just like my old Ecoboost, he was not happy doing it due to the instability of the trucks suspension. He bagged it and even put an add a leaf, but no matter what he did it was just an uneasy ride for him.
I remember when he first got it and we all were towing our trailers to an RV park in Copano Bay about 160 miles form where we live. We both left at the same time and he was keeping up with me most of the way until he had to stop for fuel. I still remember his face when he finally got to camp. His nerves were shot so I immediately handed him the beer I just opened for myself.
He ended up trading that Tundra in for a Suburban 2500 with a 6.0L that is a lot slower, but a much more pleasant drive according to him.