4X4 doesn't shift in right away, takes at least 1/4 mile before it engages. The 4X4 light will flicker on and off.

Checked the vacuum lines, one red and one black.
The black line held pressure.
The red line didn't hold pressure.

Are both vacuum lines supposed to have pressure or is one a relief or somethin?

Is the actuator bad?

Thanks in advance for any help.

 

The fork is not spring loaded. Vacuum sucks it both directions.
You need vacuum to move it into 2wd and you need vacuum to move it into 4wd.
The fork "might" stay in place with the absence of vacuum (i dunno for sure). But, you must have vacuum to move the fork either direction.
To check the lines, you'll need each end, of each line, disconnected though. You can't pressure check with any SURE success by just unplugging one end.
To check the actuator: Remove the four bolts and take the whole thing off. Hold finger over one of the vacuum ports and push the fork. It shouldn't go anywhere with continuous pressure.
Then do the same with the other vacuum port.