One problem related to brake master cylinder has been reported for the 1999 GMC C1500. The most recently reported issues are listed below.
On Jan. 14, 2000. My abs and brake warning lights came on. Both the electronic brake control module and master cylinder were defective. They were replaced by dealer. Now brakes go to floor. Pull to rt, and are mushy. I think the replacement parts are defective, but the dealer says they won't do anymore. These brakes are still defective and make the vehicle a hazard to drive.