Dangerous Stability / Traction system in Saturn Aura

I purchased a new Saturn Aura in June of 2008. The car currently has less than 15000 miles on it. The car has had numerous issues since I have brought it home. The first occurring the day I drove it off the lot. The most recent and dangerous issue is related to the stability / traction control system. Periodically when the car goes above 55mph the stability / traction control system will error out. The error causes the car to shake and the engine to want to stall out. The combined shaking and engine issue makes the car difficult to control at speeds above 55 mph. When the issue occurs the car does give off a code. The dealership does not know what is wrong. I have taken the car in twice now for the issue. The second time the dealership kept my car for 6 days and changed nothing. The dealership installed a monitor for the engine. The next time this happens all information will be recorded. The issue is dangerous, and I am fearful of driving the car. I requested a rental car until the issue could be fixed. I was denied. I was told I have to drive the car, so the dealership can figure out the problem. I contacted GM and asked for a letter stating that this issue was not dangerous and I could safely drive the car. GM denied my request. I asked GM to take the car back, this request was also denied. Essentially I am waiting for the issue to occur again, hoping the stability control system does not error while I am driving on ice etc. GM has been unhelpful and negative. I will never purchase another GM car again. This is my third General Motors car and my last. The attitudes and lack of help has ruined this car company in my eyes.