GMC Troubleshooting Questions? Ask a Mechanic for Answers
Smooth out as in how? not bouncing as much like as it shock absorbers and/or struts?
Have you tried anything at all yet?
Which Sierra is this, 1500, 2500, 3500?
Shocks and/struts will not really help that but I must ask, what are the numbers off the front and rear tires, the LT235R16 or P235R16 numbers. Those are just examples, write down the numbers and give them to me. Also, do you know if you have any factory devices that are supposed to make that ride smoother?
Do you still want help with this?