First thing is check the fluid. Is it low or have water in it?
Then check to see if it goes into 2H/N/4H/4L, it should shift smoothly.
Then check the chain, drop it into 4WD, and turn the rear while holding the front shaft.
There should be little play before the front starts to turn. It will vary dependent on mileage of course.
97 Sahara, 74 Renegade, 72 CJ5, 55 Willy's (the Beast) Boss 302, 6:34 gearing, Bose 901 speakers.
God I miss that Jeep. Forgot the kinda Jeep, 80 SX4.