shaking will turning at low speeds

Have a 2001 GMC Jimmy. Runs good, drives good. We have a really bad vibration when turning into a parking space or around the drive at slow speeds. It's been doing this for a long time but I can't stand it anymore. I checked the ball joints for play and didn't find any movement. The hub was replaced on the drivers side a year ago, other one seems fine. As I was going to park it the other day, I put it in nuetral and let it coast in. It got better but didn't completely go away. What should I start looking for? I'm not an expert and some advise would get me to check the proper things first.

thanks/

This is almost impossible to diagnose in this environment, first the 4wd transfer case could be partially bound up, or the locking differential may not be releasing, someone familiar with this condition has to road test it and actually feel what's what.