Pete,
I have a '91 Pathfinder and I have had similar problems with going into reverse. I have also had problems shifting from 1st to 2nd, and 2nd to 3rd. It's kind of like the vehicle momentarily pauses and searches for the correct gear.
I was just wondering how you made out. I am about to get the tranny and tranny cooler completely flushed and I am adding an auxiliary tranny cooler and filter in an attempt to save the transmission.
I hear that a rebuilt tranny or a remanufactured one is extremely expensive!
I'm curious as to what you found or what you did to remedy your situation...