One problem related to air brake disc rotor has been reported for the 1999 GMC Sierra. The most recently reported issues are listed below.
Trouble with rotors-8000 miles & rear brakes started to hang up & lock up. 8400 miles rotors were replaced - 29100 miles all four rotors had to be replaced again. Original factory brakes had 50% lining left - rotors were badly scored and chewed up - rotors over heated and delaminate-they are of very poor quality.