Just got back from nearly 3 weeks in Yellowstone, Cheyenne and Custer State park. It was my first time personally towing in the high mountains as a driver.
I drive a Sequoia with a 5.7L motor and I don't exactly take it easy and try to baby anything. I drive it. If that means WOT to hold the speed I want, that's what I did. My speeds were also held at the speed limit or better.
I'll manually shift at times to help hold a gear, as well as engine brake down hill. But I rarely attempt to alter shift patterns to keep RPM's low, as in below 3k...when its working hard.