Two problems related to cruise control have been reported for the 1999 GMC Sierra. The most recently reported issues are listed below.
While on the highway with the cruise control on, the consumer tapped the brakes to cancel the cruise control, but the vehicle started to accelerate. The only way to stop the vehicle was to shut the engine off.
When attempting to pass another vehicle on an incline at speeds of 55mph to 65mph the transmission shifts into second gear and revs the engine up to 4500 rpms and doesn't increase the speed because it is running at its peak speed in second gear causing me to have to let up on the accelerator and try to get back behind the vehicle I was trying to pass. This same downshifting also occurs when using the cruise control. The dealer did not want to test drive the vehicle on a similarly inclined road to duplicate the problem because he didn't have another vehicle like mine to compare it to. The defect in this transmission could easily put me in a head accident situation and needs to be addressed immediately.