Brian Monetti, I restore Camaros
These things tend to have problems.
First, make sure you are checking for the voltage when you are going into 4x4, because otherwise it shouldn't be getting volts. It will probably take two people to test going back and forth and also keep your test lamp connected. If there is no voltage changing, the problem could be with the wiring harness itself (they do go!) or with transfer case control module. Make sure you check the fuse for the TCCM as well, it will be separate from the actuator itself!
Replacing the TCCM will probably be expensive. If you are doing the work yourself, I would recommend first replacing the front actuator. Before you buy it, see if the store will accept returned electronics. If the problem turns out to not be with the actuator, you can save yourself $100 by returning it! If that doesn't do it, I would do a full visual check of the wiring harness. Sometimes problems are visible, but not always. Beyond that, its hard to really diagnose the problem. Make sure the mechanic will not charge you for the TCCM if he replaces it and that is not the problem!
Hopefully its just the actuator. The replacement ones never seem to last as long as the original, but 2 years seems a bit short. Good luck and I hope this helps!