Were you doing much backing and maneuvering in reverse before you unhooked the 5er? With minimal air flow across the OTA transmission cooler, it doesn't take very much time for the fluid to get hot. I speak from experience, I too was very concerned when I saw all that tranny fluid on the ground after maneuvering my travel trailer in reverse for, what I thought, was not an overly long period of time. Fluid looked good, leaking stopped and I towed many thousands of miles after that without any problems. I installed a Hayden six pass tranny cooler after that to help keep things cool, later swapped it for the Tru-Cool Max. This was long before the 6.0 cooler became available. About 20,000 miles after my scare, I upgraded to the BTS transmission but it too can be overheated if you do extended backing and maneuvering in reverse, even with additional cooling devices. Note, mine is an early '99 which does not have the OTW transmission cooler in the bottom of the radiator so it will get hot a lot sooner than the later models.