This morning my 4x4 has been engaging at will on its own for seemingly no reason. 4hi comes on solid and 4lo will be flashing. I have to keep hitting the 2hi button every 5 minutes to keep it in 2wd.

What are the likely culprits? Since it does switch back to 2wd, I'm assuming the vacuum actuator is fine, but I do have a new spare one just in case.

 

3-button dash switch or 4-button (auto-4wd)? If 4-button, I would suspect corrosion at the TCCM (passenger side kick panel) since the switch uses resistors to alter voltage returning back to the TCCM. If there is corrosion bridging those two contacts, it can cause what you are experiencing.