This morning it happened again while on the way to work. I shut it down to "reset" it and it worked fine for about 2-3 miles, then the MIL came on, the trans dropped down 2 gears and the rpms went up to 3100 at 70-72 mph. The MIL code read 0750, Solenoid pack.
I drove back home and checked a few things online. The symptoms indicated that the solenoid was failing or had failed so I checked YouTube to see how to change it. I had to drain the pan, pull the filters, remove the valve body and swap in a "rebuilt" solenoid pack. It was $240 with a $200 core!
It is all back together, the code was cleared and it all seems great. There was next to no grit/debris in the pan, the magnet only had a very thin film of metallic paste. I've been good about trans service.
I was impressed at how easy it was to swap out. I've always looked at automatic transmissions like "voodoo science" but this was a nice victory.