Here is the info you need to test this system.
Beyond all of these items, It may be a good idea to verify that the RADIO, and TCCM fuse are all intact and not burned. You may also want to try to remove the TCCM fuse for ten minutes to clear the trouble codes stored within to see if this restores your 4wd.
The location of the TCCM is underneath the center of the dash on the transmission tunnel. Feel free to contact me with any questions or problems! Good luck!