Loss of vacuum to my 4x4 actuator

[TD50]

I have followed all my lines and i have pressure other places but no pressure at the actuator. anyone have any ideas?? would love to get my 4x4 back. Thanks

 

[WhiteExpress]

There is a pair of vacuum check valves coming off the pass side of the intake manifold.

When my Dad's '98 had this issue, I replaced them both in addition to new rubber line / elbows. Problem went away.