Two problems related to brake disc rotor have been reported for the 1998 GMC Sierra. The most recently reported issues are listed below.
There is severe vibration when braking due to rotors that are prematurely wharping. Cause in unknown.
When applying the brakes it feels as if there is pulsation from one side to the other. Dealer says there are heat cracks in rotors and need to be replaced for 3rd or 4th time.