Vibration mystery
 

I have a 2011 z71 with 178K. I had an engine mount break and took it to my local repair shop. He replaced both mounts as well as the transmission mount. As soon as I cranked the truck after the repair I noticed the sound was a little different. It now have a vibration at around 1100 rpm’s in town as well as on and off on the highway. I took it back and had a complete tune up. Still there. You can walk the rpm’s up while in park and create the vibration but is not as bad as when you are driving. I have also noticed it worse when it switches to 4 cylinders. Any ideas? Happened only after the mounts where changed and will do it in park.