Hi, does anyone have a theory?
I have a '99 automatic Protege:

Symptoms:
1. When warm, the alternator light intermittently flashes. When this occurs, the car switches to and/or sticks in 3rd gear. Acceleration is very poor at this time. Goes away after a minute.
2. If the car is at a stop light when the alternator light flashes, the transmission will jerk when pulling away (forced switch to 3rd gear?).
3. While stopped at light (in gear,) the RPM may bounce between 750 (normal idle) and 500 (lights also dim at this time) and alternator light may flash on.
4. Moving the gear selector to 2 or 1 does not switch to the lower gears while the problem is occurring.

Notes:
1. 100,000k’s, not a lot of maintenance, except for oil and filter changes.
2. Always starts ok, and runs fine 90% of the time.
3. New battery installed
4. No loose battery cables
5. Transmission fluid is full
6. Cleaned throttle body and MAF sensor
7. Mazda dealer has done a basic electrical check, all ok (alternator putting out 14.5v).
8. Mazda indicates no error codes are stored in computer.
9. The check engine light does not come on (light bulb is ok).