It's not the reverse solenoid - which I guess is a good thing.

It's an intermittent solenoid issue - I would have to check the diagnostic to see which one - I get the Trans Failsafe Prog on start up and the car has one forward gear (4th, so it's still ok for the highway). After a warmup (clearing the filter?), I can restart the SAV and the issue is cleared. I'll be investigating local tranny shops and seeing if they have the necessary skills to swap out the solenoids.