GMC Troubleshooting Questions? Ask a Mechanic for Answers
Check the shock absorbers. Go around to each of the 4 corners of the vehicle and press down on each corner one at a time and get it bouncing and then let go and watch and count the bounces until it stops. 3-5 bounce is ok. Any more and the shock is weak. Do this on each 4 corners to check each shock absorber.