This is a follow up to the original conversation found here:
The local transmission shop said it's working fine and to bring it back when acting up. The light would come and go occasionally until last week when the last gear finally refused to engage at all. I brought it back today and the man says he took it for a ride and hooked up the analyzer at the same time. The computer is sending the message to shift but the transmission is not doing so. We decided to drain the system continuously and add fresh fluid until all old fluid is gone. He also dropped the pan to clean the screen.
The report is this: there are metal shavings on the bottom of the pan, similar to flakes. The solenoid has already been replaced by someone else -- the dealer. The voltage to open and close the solenoid is there. He thinks the valve is gummed up or something and says it's not worth the cost to drop the transmission and fix it. It's possible the torque converter is going bad. He suggests the new fluid and a valve lubricant and crossing my fingers. The transmission does shift smoothly into all other gears.