... with the engine shut down and the throttle minimum [not cranked up at the dash either] I found that I could pump it up to the pump's usual 15 to 25 but it would quickly drop and eventually go to zero. So in order to get a quantitative measure I timed the drop from 10-in to 5-in and this time was 25 seconds.

This is entirely consistent with what my understanding of the function of the VCV and that is to trigger/regulate a variable vacuum signal to the tranny modulator that simulates throttle position [ demand/load ]. The time it takes for the VCV to bleed down my static vacuum from the pump or to act as a bleed to the dynamic vacuum that is fed by the engine's vacuum control system [through multiple restricted orifices] is no doubt adjustible, at least on those VCV(s) that are designed to be adjustible.

My engineering sense of the above is why I initially chose to start this THREAD and also why I selected the title as I did, for I saw that the VCV might very well NOT be adequately adjustible IF it were fed too strong a vacuum... thus the need to restict the vacuum using the various sizes of small multiple plastic orifices and in the 1981 and later models, I'm now convinced that the inlets and outlets of the small dashpot chambers very likely also serve as restrictions. I am more than ever convinced that the balance of ALL the restricted orifices is IMPORTANT if not CRITICAL to being able to properly set up [" balance "] these vintage engine/tranny vacuum control systems AND certainly CRITICAL to maintaining a reserve of vacuum strong enough to operate the brakes IF there is a rupture somewhere in these less-than-critical vacuum using/consuming systems.
Regards,