The real eye-opener is if you use them under prolonged slow speed four-wheel-drive conditions. I promise you, and especially in the Toyota, you will want to use 4WD low WAY more often than ever before, and in conditions way more mild than you think you will need it. Basically, if you are in any conditions in 4 high where the torque converter is unlocked, you will generate tremendous heat and you will need to stop constantly to let it cool down, or alarms will be going off. The Tundra was really really bad. Not a mountain hunting truck in any way imaginable.
One should never use 4H in mountainous conditions or on severely inclined terrain, regardless of the truck or transmission. In those situations, you absolutely need to shift into 4L.
Overheating in those cases is usually caused by improper use of the vehicle. It has nothing to do with whether it’s a Ford or a Toyota. You can even damage a 4Runner, the most reliable SUV, the same way.
4H is intended only for relatively even, flat surfaces such as dirt roads, sand, or wet terrain. Even then, you generally shouldn’t exceed 45–55 mph.
I used to have a friend who worked for BP in Central Asia (Kazakhstan or Turkmenistan) as a geologist. BP provided him with a Toyota Hilux, an exceptionally reliable truck. He had to complete a full-day training on off-roading, proper vehicle use, and general safety protocols.
One of the rules was that as soon as he got onto a dirt road, which covers much of the Eurasian steppe, he had to engage 4H. However, whenever he encountered visibly uneven terrain or mountain paths, he was required to shift into 4L. There were also multiple instruction stickers on the dashboard reinforcing these guidelines.