4 wheel drive problem '97 ram 1500???

4 wheel drive works, then will pop out of gear. If I mess with the floor lever it will go back in at times. Is there a switch in the shift linkage that activates the vacuum module on the differential housing?

Here is a thread from a guy having a similar problem:
https://board.moparts.org/ubbthreads/show...e=0#Post4865796