TRANSMISSION UNEXPECTEDLY DOWN SHIFTED HARD. VEHICLE HAD TO BE TOWED- HIGH RPM/LOW SPEED/HIGH TRANSMISSION TEMPS. DEALER STATED THIS IS A KNOWN PROBLEM WITH THIS TRANSMISSION – CONTROL VALVE BODY. TRANSMISSION DOWN SHIFTED HARD CAUSING REAR TIRES TO CHIRP. FORCE ON DOWN SHIFT WAS INTENSE AT 25MPH. IT WAS SO INTENSE MY WIFE AND I THOUGHT OUR VEHICLE WAS REAR-ENDED. THIS IS A HUGE SAFETY ISSUE. THIS COULD HAVE BEEN TRAGIC IF I WAS TRAVELING AT HIGHER SPEEDS OR TOWING MY 5TH WHEEL TRAILER. PER DEALER – THIS IS A KNOWN TRANSMISSION ISSUE WITH GM/CHEVROLET. NO REPLACEMENT PARTS ARE AVAILABLE. MY VEHICLE HAS BEEN SITTING AT THE DEALERSHIP FOR FIVE WEEKS NOW. THERE WERE NO WARNING LAMPS, MESSAGES OR OTHER SYMPTOMS PRIOR TO FAILURE. TO SIDE ON CAUTION, GM/CHEVROLET NEEDS TO RECALL THESE VEHICLES BEFORE SOMEONE GETS SERIOUSLY HURT AND/OR KILLED. I’M TOLD GM/CHEVROLET/ALLISON REPLACED METAL BALLS WITH PLASTIC BALLS IN THIS VALVE CONTROL BODY AND HEAT IS SHRINKING THE PLASTIC BALLS CAUSING THE PROBLEM.