Seems like a lot of confusion just can say I tow differently now than I did in the last century. Back then the best instruments for towing were a vacuum gauge and a coolant temperature gauge. And had to add big tranny coolers because a THM 400 did not have lockup.
Today I have a '12 Jeep that is instrumented out the tailpipe. When towing the TM I limit myself to 65 mph, use the cruise A Lot and while watching coolant, oil, and trans temps, also drive to stay in lockup and out of Performance Enhancement. To do this I monitor the load factors and drop a gear before dropping lockup or entering PE.
My temperatures all are usually between 180 and 190F (180 fast opening thermostat)
and only close on 200F in a hot soak condition (off the I'state and at a stop light - have to watch thermal inertia).
Since am only turning 4800 at 65mph (6400 rpm redline) in second I can drop A Lot of gears without slowing down.
Modern cars have very wide torque bands and the key to both running cool and good MPG (I get 17-18 with the TM in tow) with a gas engine is to stay in lean cruise as much as possible. Even uphill.
