general problems of the 2004 GMC Yukon

2004 GMC Yukon while driving at normal speeds this vehicle will have a warning light come on that says "reduced engine speed" then it shuts down to 30 mph instantly. There is no time for reaction. This problem occurs intermittently. It has happened over 50 times! a few of the times almost resulted in fatal consequences in high traffic. Took the vehicle to the dealer. They said it was the throttle body. Replaced throttle body and the next day had the same issue. Took it back to the dealer, they said it was now the accelerator pedal assembly. Replaced the assembly and two days later had the same problem. Contacted GMC by phone and was basically told that there was nothing they could do because my vehicle wasn't on the safety recall list. I really need some advice or help before it costs my wife and four children their lives!.