Just did that this spring. Actually hit a couple of the cooler days, campgrounds were already closed. DV to Lone Pine was a killer. I unhooked the towed, and transmissions temps still ran over 220* (scangaugeII). Then going down, the Transmission temp got around 240*. going up again, it barfed! Stopped at the top. TF dripping on exhaust pipe makes a lot of white "smoke". Someone said it was not bad to Lone Pine, they were right, nothing to speak of. Later, going up the grade south of Bishop, 10 miles @6%, TT leveled out at 210*.
Brought her after that, after adding 1 pt of fluid, with no problems in 100+ weather on I40 going East of Barstow. Changed the 18qts of fluid and added a second cooler. No signs of a leak, maybe came out a vent.
'01 National RV Tropi-Cal, Ford V10, '01 Suzuki GV 4X4 Blue Ox Tow Bar,300 Watts Solar, 2500 Watt '458' Inverter, NO TVs, Most light fixtures upgraded to LEDs