Service 4WD Selector switch not working

[SG swoles]

Hey ,

  so I’ve been chasing this problem for months now. 2016 Silverado and the 4wd switch intermittently works. 
There’s really no rhyme or reason to when it works when it doesn’t. 
I can switch the truck on and it immediately throws the service 4wd message , switch it off and back on and it might work, might not. Sometimes it works flawlessly...
Ive found a ground wire on drivers side chassis, cleaned and reinstalled. I’ve put in a new 4wd selector switch and still same problem.  Apparently according to the dealership it’s not throwing any codes. 
I’m hoping someone can point me in the right direction here. my next step is to replace the 4wd actuator. 
 
 Also, when it it does work if I use the auto or 4wd setting you can feel and hear a  slight vibration coming from the front. Especially in the 40-50 mph range and in deceleration.   I’m not sure if that normal drivetrain noise . I wonder if the actuator is not fully engaging.
If anyone can point me in the right direction I sure would appreciate it. 
 

thanks 

[rlcole321]

could be an encoder issue in the drive motor on the transfer case that changes to and from 2WD, 4WD Hi, 4WD Lo, I've had that issue with an older GM 4WD truck.