Ten thousand miles ago I had a transmission shop install new bearings and 3.73 gears in my manual Z28. Now I have a noticable clink when giving light pedal pressure and vibration at high revs. I dropped the driveshaft to check u-joints which are ok. However, the input yoke on the differential can be rotated a couple of inches before it engages making a clunk when it does. Gear oil is very dirty. What could have caused this? What should be replaced? How responsible is the shop that did the work?

 

Take it back to the shop. It's a faulty install.