My 1999 jeep grand cherooke runs great but feels sluggish or slipper in the rear.?

[newyorkstudent81]

It's really weird. It just feels like something is loose in the back. I don't know if it's the springs or a bearing going bad. When I go from park to reverse or drive, I hear it too. That noise when shifting gear I think has to do with the car sitting for a while. It driving like it has is bad. Any ideas. Going over bumps or turning just feels sluggish and lose, especially in the rear. Thanks.