Automatic Transmission problems of the 2003 Chevrolet Express

Contact owns 2003 Chevrolet Express g3500 passenger van. The van will accelerate on its own sporadically. This started around 7-20-05. It does it while stopping at stop light and it will also do it while driving on the highway. The idle speed control motor, throttle position sensor, cooling sensor, ecm, and the prom have all been changed within 5-6 weeks. He says it did it at any speed sporadically. He made an appointment to bring the car in again for a possible repair. The check engine light will usually come on after an incident.