Thanks to all for your responses. To answer a few of the questions; I don't reverse faster than 5mph or so, I have a 100yd driveway that must be driven in reverse upon occation.
I will try to find a reputable tranny shop to diagnose the problem, thanks Rich for the insight.
OK!! While driving in reverse (without reving the hell out of it)the tranny just stops reversing and finds (a false??) neutral at which time I ease off and the vehicle stops...it then re-engages reverse. I'll try to get it to do it again today and listen/ feel for more clues.
My 80 pops out of reverse when reversed for more than 25 yds or so and then re-engages. The shift lever doesn't move. It has 137k mls and has been well maintained and is not low on AT fluid. Any thoughts.