A friend of mine just put a new tranny in his truck. It turns out on his truck,(it's a diesel with the auto) that ford puts a low tranny fluid cutout in it. When the fluid gets too low it shuts down in reverse to let you know. He didn't, pulling his 35' horse trailer to a show he blew the tranny. None of the idiot lights ever came on to indicate a problem. However he is in litigation with a local quick change oil shop because he had the full service every three thousand miles. The most recently was a week before he left for his trip. What's the saying, you get what you pay for. Hope this helps, don't know if it's related to your problem but definitely food for thought.
T. Roberts
UFD Local 1147