Another update. I recently finished another cross-country (North Carolina to California and back) trip towing a ~5700lb (dry weight) travel trailer and can confirm that, at least for my situation, the stock transmission cooler is quite sufficient. I only saw the temperature go above 180 degrees on 3 or 4 occasions. The highest it got was just a little over 200, and that was only very briefly on I-70 Easbound west of Denver climbing the first of 2 10,000+ ft mountains. The other couple times it topped out at around 190-195. The trip went over a LOT of big hills, as you might imagine, and many of them were in 90+ degree heat. I can confirm that the Tahoe (2021, 5.3 V8) was more than up to the task of an 8600+ mile round trip. No issues at all. It's a *very* comfortable way to go across the country carrying 4 people and 2 dogs.