1991 Pontiac Grand AM 2.5L mileage: 93,000. My car has a 3 speed automatic transmission with overdrive. The overdrive kicks in above 45 or 50 mph automatically. When traveling in overdrive for a long period (half an hour or greater), the transmission will not shift out of overdrive when slowing down or coming to a stop and the car stalls. Upon restarting the car, (in neutral or park) the transmission is still in overdrive. In order to get the car out of overdrive, I have to rev the engine and drop it into drive (not good). Do you have any idea what might be causing this?
Your car has a lock-up torque converter in the transmission. It locks-up only in high gear. It is supposed to disengage at lower speeds. Yours is not disengaging. There is probably a valve in the transmission "hanging up". Having the transmission serviced with new fluid may help the problem. Next step, the valve body will have to be removed and cleaned.