What year Jeep do you have? Is it shift on the fly or locking hubs? I have a 92 YJ.. Shift on the fly isnt really "on the fly" You can do it while you are moving, but you must put the clutch in and let the engine rev down. Give that a try. And also, when you are in 4wd, the shifter always feels a little more sloppy. But if gets really bad, maybe you should take it in and have them look at the T-case.