BRAKE VACUUM PUMP LOSES PRESSURE WHEN BRAKES PRESSED REPETITIVELY. WHILE IN TRAFFIC I REAR ENDED ANOTHER MOTORIST DUE TO BRAKE PRESSURE LOSS. CAUSING DAMAGE TO BOTH VEHICLES. NO INJURIES DUE TO LOW SPEED BUT EVEN AT HIGH SPEEDS BRAKE PRESSURE IS LOST, IF THE BRAKE PEDAL IS DEPRESSED REPEATEDLY YOU LOSE ALL BRAKE ASSIST. VEHICLE WAS BROUGHT IN FOR RECALL REGARDING ABS SOFTWARE UPDATE BUT BRAKES STILL FEEL HORRIBLE. TSB WAS ISSUED TO VEHICLES UNDER 72000 BUT ONLY BEGAN THIS YEAR. CURRENT TSB DOES NOT COVER MY VEHICLE. I CONTACT THE GM REGARDING THIS ISSUE AND THEY TOLD ME THAT THEY WILL NOT COVER MY VEHICLE ONE MAKE EXCEPTIONS.THIS NEEDS TO BE A FULL RECALL OF THE VACCUM PUMP, VACUUM LINE AND MASTER CYLINDER LIKE STATED IN THE TSB. SOMEONE CAN DIE FROM THIS ISSUE IF GOING DOWN HILL AT SPEED.