How many miles on the Jeep?
There's the obvious stuff that I have to say:
- Make sure your tire pressures are matched front to back and side to side.
- The tire/wheel combination among all four wheels needs to be identical to reduce the amount of difference between front to rear revolutions at speed. It's important to run the same tires front to back and they should be rotated often. ChryCo doesn't tell you that but then they are ChryCo... Kwality with a capital K.
- Ensure that there is no binding in the front prop shaft u-joints. If they haven't been maintained properly and are sloppy and/or have more than normal drag on them with revolution this can add a form of preload to the front prop shaft which the mechanism has to fight to release into 2wd.
If you are further along with that I'd take a look at the shifter to make sure it is aligned properly and travels properly through the interior bezel.
Failing that, it might be time to pull the case and inspect the internals. It could be something as simple as the teflon pads for the shift collar forks being worn or even missing (Bt/dt).
HTH