I have a temperature probe in both the output line and the tranny pan. The temperature in the pan normally hardly warms up at all as wittmeba noted above.
The temperature at the output line reacts quickly to things like stop and go traffic, and spotting a trailer in a park site. I am convinced that you will burn your tranny down completely before a temp probe in the pan alerts you to over heating.
When my output temperature starts climbing past 235 it is time start changing or stopping what I am doing.
My tranny is custom built for towing with a tight torque converter, so in stop and go traffic I place it in neutral. It valve body has been modified to circulate fluid while in neutral. Towing on the highway with the torque converter locked I see 170 or so at the output line.
I wonder about all the people that have no way to monitor this and do not know the conditions they can easily subject their tranny to.
Chris