Good post. I have a 2011 Tahoe without the factory external trans cooler. I added a 40K transmission cooler plumbed after the factory in radiator cooler. I’ve been thinking about adding a thermostat between the radiator cooler and the external trans cooler. I’ve ran it for 40k miles without the thermostat but my trans only gets to about 140° when not towing.
My hottest temp while towing on a 95° day was 198° In the middle of the day in traffic. It stayed there for about 5 minutes and went back down to its normal towing temp around 180°.
Love towing with my Tahoe.
Thanks!
Jeremiah