Have you checked the fluid? How are you shifting?
If the fluid has been changed recently and the TC is full, try this trick when shifting in/out of 4wd. Let off the accelerator, shift TC into gear, slide tranny to N, blip the throttle, slide tranny back to drive, blip throttle again. I normally do this between 5 and 30 MPH and can feel the TC lever click once its completed the shift.
2000 WJ 4.5L - Stroked, Locked, & Long-Armed
Looking for 6" WJ springs!