Well actually they have hubs, they are just auto locking hubs, but the wheel bearings are built into the hub assembly. Same thing though. But that wouldn't be your problem. Wheel bearings will make the tires shake and move, but it wouldn't cause 4x4 to unengage. You need to check the auto-locking hubs and find out if they are bad. Now that I have thought about it that might be your problem. If they are bad they wont fully engage and cause 4x4 to work incorrectly. The second thing you can do is replace the engagement motor in the transfer case. You might do that first and see if it fixes your problem. If not go back to what I told you to do first.
As far as the driveshaft goes, if there is no excessive play, then it shouldn't be a problem. Check the yoke on the driveshaft make sure it's not loose. Replace that fuse, and don't worry about the fluid for right now.
Let me know what you find
2004 Lv II, 3' BL, AAL, 6400 Shackles, Maxxed T-Bars, 33x12.5 BFG KM2 Mickey Thompson Classic II's. Billet Grille, Chrome Bug Guard, 06+ Chrome mirrors +06 badges. Dual CB antennas Edelbrock performer IAS shocks.
5.0 swap M5OD 5 speed AWD, MPT Tuned!