WHEN VEHICLE MAKES SHARP TURNS OR STOPS QUICKLY THE SEAT BELTS DO NOT LOCK, AND PASSENGER COULD BE THROWN INTO THE DASHBOARD WHEN BELTS DO NOT HOLD. BELTS THAT ARE CONNECTED TO THE DOOR ARE DEFECTIVE, DEALER AND GMC AWARE OF THE PROBLEM. VEHICLE HAS EXTENDED WARRANTY. PROBLEM STILL EXISTS. PROVIDE FURTHER INFORMATION. *AK