"The factory transmission cooler is a separate unit in front of the radiator on my Ranger, so therefore it should not be dependant on the thermostat but it did make a difference. Go figure."
My 98 Ranger 4.0L V6 has both the factory external transmission cooler on the front of the radiator AND the relatively standard factory transmission cooler in the bottom of the radiator. It also has a power steering cooler. These, plus the "camper adapter relay" for running and brake lights lead me to believe it has the factory tow package, but I can'd find a code for it.
AFAIK, the only vehicles I have ever owned that didn't have a transmission cooler in the bottom of the radiator were manual transmissions.
You obviously never owned a Rambler as they were air cooled transmissions on them. The bell housing was slotted and finned for cooling air around the torque convertor. As an afterthought, the early transmission fluids were mineral based with a lot of additives that separated under excessive heat and solidified into black goo. The newer transmission fluids are mostly synthetic and if you get really picky, you can extensively flush and change o rings inside the transmission to flouro-silicone and use pure synthetic turbine oil Mil Spec 7808 Harold