DURING NORMAL DRIVING, BRAKE PEDAL WILL SOMETIMES GO TO THE FLOOR WHEN ATTEMPING TO STOP, AND VEHICLE WILL NOT SLOW DOWN AT ALL. AFTER SECOND ATTEMPT, BRAKES START WORKING AGAIN. NO ERRORS REPORTED BY VEHICLE COMPUTER. WE HAVE ALREADY HIT A MAILBOX TRYING TO AVOID A CRASH, AND ALMOST ROLLED OVER ANOTHER TIME DUE TO NOT BEING ABLE TO SLOW DOWN IN TIME. TWO GM DEALERS HAVE FOUND NO PROBLEMS, AND WE HAVE BEEN TOLD TO NOT BRING THE VEHICLE BACK TO THEM AS THEY SAY NOTHING IS WRONG WITH IT. PROBLEM HAPPENS APPROX. EVERY 5 WEEKS, NO CONSISTENCY OR EVENTS LEADING UP TO BRAKE LOSS.