One problem related to carrier/rack has been reported for the 1999 GMC Sierra. The most recently reported issues are listed below.
Odd noise from vehicle. Stopped and noticed the center of the vehicle was low (box and back of cab were in contact at the top and separated by several inches at the bottom. Looked at frame and saw that right side of frame was rusted and is cracked almost all the way through, allowing frame to sag and presenting the danger of frame separation which would cause an accident.