Clemson - I think we are in agreement too. Here is my hands-on experience: On my 81SD I had an indy replace the transmission. I tested it by unhooking the plastic line from the VAV to the tranny and I plugged that line into the Mityvac so I could pump some vac to the tranny. Upon driving around I found that the upshifts were good and smooth - no vac. However the downshifts were quite clunky.

So I drove around more and tested the downshifts by pumping up some vac before coming to a stop. Applying vac got rid of the clunk and I got a smooth downshift.

I was never exactly able to figure out the vac modulator or its purpose other than to read that adjusting clockwise gave you a firmer shift and counterclockwise gave a softer shift (could have that backwards - do not remember). In fact I adjusted the vac modulator several times and do not recall feeling any vast change. And I think you are saying that the vac modulator clicker will adjust how much or how little vac it bleeds off when you downshift.

Clemson - your post sounds right and I think I just plumbed and compared the two extreme opposites - vac and zero vac.