A little update. I hauled it home from the beach, and took it the trusted transmission shop. He plugged in and pulled the codes, and I forget the numbers...but it showed a shift solenoid malfunction. He cleared the codes, and added almost a quart of fluid and said to drive it and see if it sets another code and turns the light on again. He said it should do it within a hundred miles or so, if it was going to. He said these transmissions are very finicky about being even slightly low of fluid, and that I may get lucky and that caused it. I've run the hell out of it for a little over a hundred miles, and it's still fine. I'm gonna run it some more and see, but so far....so good!