Following up for FYI and anyone that may have been wondering..
I ended up not installing a cooler or doing a flush/fluid change of any kind.. The only thing i did was add a hitch and pulled the trailer. I had 800lbs of people, pets, and stuff in the car and the trailer weighed ~3500lbs (a lot more than expected), i pulled it 3300 miles in 4th gear, rarely did the car hunt for 3rd. It never overheated and did spectacular at 70mph. On the whole trip I averaged 16mpg (mileage/fuel calculation). I anticipated hills, stopping, slowing, and even ran the car hard a few times to merge in to traffic.
There is absolutely no reason I believe a trans cooler would have been needed and aside from the cost of fuel and boredom of the trip, I wouldn't hesitate to tow the same trailer across the country again.
And when I dig the cooler, thermostat, and extra hose out from the middle of my garage full of household goods, i'm going to post it for sale...what a waste of money.