Towing Basics

Ok, I just bought a TM 3124 and towed it from Casper Wyoming to Denver. It towed like it wasn't even there with my V6 4runner, with it's 6000lb towing capacity. I have towed a lot over the years so I know that once I head UP I will see more issues but I plan to take it easy.

My questions are:

1. When is the transmission most stressed, at a constant 3000 RMP and constant speed, or a lower RPM and shifting around. (Auto Transmission)

2. Is it my transmission that is stressed in carrying a big load, or is it more my engine?

3. I am never in a hurry while towing, and am happy behind the slow semi's, so what is the rule of thumb to tow big loads, while trying to be as gentle on the TV as possible?

Thank you,
Jason