More than likely I am gonna say that its one of the 5 switches on the top of the transfer case that has gone bad, or the transfer case actuator itself. There is a little black case a little bit bigger than 4"x4" I am guessing. And it moves the shift fork around in the transfer case. I would lay underneath and have someone move the 4wd shift lever back and forth through the range to hear if that is moving or not.(Make sure its in park though...lol) And if thats working then my guess is one of the sensors on the top of the transfer case that will need to be replaced.