1995 Oldsmobile Aurora Automatic transmission

1995 Oldsmobile Aurora mileage: 150,000. I had the transmission rebuilt by a reputable dealer. After one week the service engine code light came on and the transmission jerked very roughly when put into gear. They diagnosed that a circuit that went through the ignition switch was the culprit. They changed out the switch. That solution lasted about three weeks before the code came back and the transmission bucked. They took the car, dove it for about two hundred miles but the problem did not reoccur for them. But it happened again yesterday. They removed the code, the same code that told them the ignition switch might be the problem, and the car runs fine. This problem occurs only when starting the car, never when in operation. Any suggestions?