This is common for the NP242 transfer case. The shift fork is not fastened to the shift shaft. It's floating and a spring makes it move when all is right. I have a 06 CRD KJ and a 00 XJ both with the NP242 transfer case and they both act the same way.
As mentioned your tires should be all the same brand and wear and inflated the same. But that does not work for my two
Here's what works for me every time on both of my jeeps

While moving instead of going straight from full time to 2 WD, pause in part time for about a hundred feet then shift to 2 WD

Works every time for me. For me nothing else works

Backing up does not do it, bliping the pedal does not do it, shifting to neutral does not do it, shutting it off over night does not do it. My CRD as far as I can tell will stay in part time forever when shifted from full time to 2 wd.
I suspect that ATF is not the best thing to use in these cases but have not tried anything else. I did a couple of searches on the WWW and found another vehicle maker uses the same or similiar transfer case and they don't use ATF in them. Maybe 10W motor oil or something, I don't remember for sure.
Joe