So I finally got around to getting the VCV back on the car so I could test it while it was hooked up to the car's vacuum pump.

The gauge read 15 at idle and as I actuated the linkage lever the reading quickly dropped to 0. Now I'm thinking the VCV is probably ok.

It got dark before I was able to get the linkage attached and take the car for a drive. I'll try and test drive it tomorrow and monitor the readings.

I gave the main vacuum line a good inspection and can't see any potential leak sources. I'm wondering if maybe the brake booster is leaking and this could explain both the intermittent failure of the power brakes I have experienced in the past as well as the shifting harshness. Anybody know how to test the brake booster for leaks?