I just picked up a '63 Grand Prix. Yesterday, every time I slowed to a stop, the engine died. It seems the trans won't disenagage and kills the motor. This was verified by jacking up the rear end and placing the trans in drive, the motor would stay running. On the ground, when placed in drive, the motor dies. Any ideas on what would cause this? I ran a search on the slim jim transmissions and the comments seem to be to switch to a 350/400 trans.