I have a 2021 GMC Sierra SLT X31 a beautiful truck. While driving the highways if you hit a bump or rough road the Vehicle Shimmy'* in the rear end and some vigorously the the rear moves from side to side. I have called GM, taken it to (3) Three Authorize Dealership, and they all come back with the same answer that all bolts are tighten to Spec. Ok I get that, but that doesn't solve the problem. Are there anyone else out having the same problem, and how do I correct it. I also change the tire out that didn't help. i need help

With rear wheel drive vehicles, rear-end hop can occur when going over bumpy roads and you stay on the throttle. Try letting go of the throttle the next time you see the same rough terrain and see what happens.

Thank you for the reply, most of the time I can not see when the terrain will change. I've never had an issues with a Vehicle does what my truck is doing. Is it a suspension issue that make it hop/bounce over bad road?.

What does it do with you bouncing it in your driveway?

Traction is like a checking account. You have so much available, but if you over-draw then you'll go sideways. In your case, your checking account is having a bunch of funds removed while the rear wheels are unloaded during the bumps. Letting off the gas is like writing one less check.

If you have to, find a bumpy stretch, turn around, go back far enough, turn around, get up to the same speed as you were at before, let off the gas before the same bumpy stretch.

Does this change it?

What other vehicles have you driven?

Regarding your question:

Yes and no. We're guessing that you are in a heavy duty two-wheel-drive vehicle that has a majority of its weight in front and an empty bed in back, and while you're going over bumps and accelerating or maintaining speed the rear end kicks out a little. I bet if you put load the bed with half the payload rating of bricks/boards/whatever, the issue will go away or at least diminish quite a bit.

No Sir the truck is a 4 Wheel drive. As long as you are on smooth surface the truck drive great, but as so as the road get rough it Shimmy in the rear. My 2009 Alvanche drove 100 percent better than this 2021 GMC. So I'm guessing Noone else are experiencing the problem that I'm having.

I guess it'* to much trouble to bounce it yourself to see what happens.

Is it in 4WD or 2WD when you are having this issue?

The symptoms you are describing lead to either how the vehicle is being driven, or the rear shocks are faulty or inadequate for the vehicle.

Take it to another dealer if you can and get another inspection on the rear end.

Thank you Mike for your input. I have taken it to Three dealerships, and no ones seem to care. It is if they are covering something up. The truck has the Rancho shocks. I can't get a dealerships to begin eliminating things to find the real problem . A brand new truck that drives like crap the worst driving vehicle I have ever had. I can't do any or it will Violate my Warrenty. What should I do? Only 6000 miles to date.