Throttle Control Warning Light On problems of the 2008 Chevrolet Impala

I have a 2008 chevy Impala. Starting last month (may 2013) the service traction light and reduce engine power lights started coming on. I took it back to the place where I purchased the vehicle and it came back that it was the accelerator pedal. It was replaced and 5 days later the lights were back on again. I called the shop and they told me to bring it back to them on Monday because they were closed Saturday and Sunday. I took the car back to the shop and the lights weren't on. They told me that they could not get a reading on the car and to come pick it up. I drove off the lot and 3 days later the lights were back on. This has happened every week since they replaced the accelerator pedal. When I took it in initially they said it was either the accelerator pedal or the throttle. On Friday June 14th the car stopped the service traction system light, reduced engine power light and starting disabled service/check throttle light came on and the car stopped. It was still running but when I pressed the accelerator pedal it would not move. I cut it off and sat for about 10 minutes. I started it and drove straight to the lot it was Friday at 4:45 pm they closed at 5:00 the guy said bring it back Monday (wow really). I parked the car again all weekend didn't start it until Monday. The lights were off when I got in it on Monday as soon as I backed out of my drive way the lights popped back on and it would only go 40 mph. Luckily the place is about 3 miles from my house when I got there they weren't open yet so I sat there. When they finally opened I drove in and told the guy who I was. The drove the car around several times and could not get the lights to come back on. It is now Tuesday and I still don't have my car back. They say that they took it to the dealership to have them look at it. I'm not sure what to do at this point I need my car to get back and forth to work.

The contact owns a 2008 Chevrolet Impala. The contact stated while driving 65 mph, her vehicle stalled. The contact had to maneuver through traffic in order to avoid a crash. The auto throttle body disabled light illuminated on the instrument panel. The contact did not try to restart the vehicle. The vehicle was towed to her home. The vehicle was taken to the dealer who determined the accelerator sensor malfunctioned. The vehicle was not repaired. The manufacturer was not notified of the failure. The failure mileage was 178,000. The VIN was unavailable.