I don't have a temp gauge and my older Scan Gauge does not have transmission temperature as a display option. I am working to see if I can upgrade.
The only indication that the transmission was hot was that the cooling fan was cycling on and when leaving after lunch it didn't seem to shift correctly.
When pulling onto the freeway there was no power, it was like in a lower gear and would not accelerate. Like the engine and transmission said...we are going on strike. Had this happen to another Motor home pulling out of Death Valley on the West side, hilly, curvy and hot. Engine was not over heated. But transmission was not happy. That is my only reference point.
I don't understand exactly what Tow/haul does. I try to use it most of the time, but was experimenting to see what seemed to keep the transmission happy so we could limp home.