4 Wheel Drive/SUVs: 2005 GMC Sierra 4WD problem, gmc sierra, button works

Question
The push button 4WD controls do not seem to work properly, if you shift from 2hi to 4hi to 4low it will not let you reverse the process without shutting off the truck and restarting. There is also a loud clunk when it does shift from 2hi to 4hi then to 4 low. Not sure the Auto 4WD button works at all.

Answer
Gm has had alot of problems with the electric motors on the transfercase. That is more than likely the cause of your problem, however I have tore transfercases apart and found that the forks are wore or the plastic fork covers are wore preventing it to shift in and out of 4x4 with ease. Hope that might help you a bit, thanks ADAM