transfer case question

I have a 1995 jeep grand cherokee and I know this is a cherokee forum but I was told that they are the same t-cases. Its the t-case with 4-low and 4-part time nothing else. I will engauge it and drive for a while and I have a screen that usually has all 4 wheels lit up. But all of a sudden it won't be lit up and sometimes will disengauge itself not smoothly course since im doing around 30-40 miles per hour and it will just start grinding...What should I tell my mechanic to look for, I would do it myself but its too dam cold and I am suppose to be getting a lot of snow. Any help is appreciated.

Sounds like a linkage adjustement issue.