One problem related to brakes failed has been reported for the 2003 GMC Sierra 2500. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2003 GMC Sierra 2500 based on all problems reported for the 2003 Sierra 2500.
Brake failure upon slowing down at off ramp. Avoided accident but had total brake failure. Pulled into parking lot, checked fluid levels, were ok, tried brakes again and they were working. Have not had a problem since. Have heard reports of similar nature. Some think it is a problem in the valving. Hope you can find a cure.