Got my truck back and had to go to another dealer because the one I bought it at said the truck is performing as it should. I now went to second dealer but they feel the shake and that's within spec. I told him I'm not buying it and contracted GM directly. I was assigned a rep and going to a third dealership to see if someone will feel what I feel. I almost feel that these people think I'm lying. I'm at the end of my rope with this truck I keep explaining to the service managers I feel and hear something in the back. I also tell them I'm going deaf from serving in Afghanistan and Iraq and I know I need hearing aids so if I hear something that means its loud.