We have a 97 Grand 3.8 with 120000. It stalls when we shift into reverse. If we really tromp on the gas in forward, it will go until we slow down to stop. Then it stalls. We have cleaned the throttle body. Put on a MAP sensor. Used fuel additives, and cleaners. Ignition codes only shows 12 and 55. Any help would be appreciated.

 

If the engine is stalling any time you come to a stop, than the torque convertor is probably staying locked. You'll have to remove the transmission to service the torque convertor
and with that many miles I would have the trans overhauled while it was out.