Thanks Frank. At one point, I thought I had it licked, but the next day it was back to the old tricks. I didn't replace the sensor with a new one, but I did test it before installing it, and it was working properly.

But even if I bypass the sensor and ground the wire leading to it to the engine block (which is what happens when the switch turns on), it still doesn't shift.

I've got the Chilton's again. I'll work on it today.