I have replaced the transfer case motor, replaced transfer case control module, replaced the actuator and I still get the message about service 4wd. Yeah also replaced the 4 button selector. All parts were replaced with new parts not used. What else could there be to do? I have a 05 suburban z71

 

Does the 4wd work?
Are the lights on your new switch staying on?

 

At first the lights came on and showed 4L. The new motor wouldn't engage to make a switch out of 4L.
After 3 attempts of trying to switch out of 4L, I turned off the vehicle then tried again but this time the lights on selector gage wouldn't stay on and hasn't stayed on since. The lights will flash on the gage when you crank car but goes off shortly after.

 

Man.......I'm surprised no one has chimed in yet. I read about some module on the trans case, I can't remember for the life of me what it was, but it sounded similar to the problem you're describing. Sorry I can't be more help......maybe if it was right in front of me, but over typing I don't want to jump to any conclusions ya know....The only other issue would've been your switch but you replaced it so .......:|