You do not need vacuum for upshifts as I remember, only for downshifts. Isn't that right Kerry?

Tee the Mityvac in like suggested and do the reads. Then you can just connect the Mityvac to the tranny by itself. As you are shifting up it should be smooth with no vacuum. When you get ready to come to a stop, pump up the Mityvac and it should downshift smoothly. It has been 2-3 years since I got mine adjusted (with Kerry's help) but that's what I remember.

In normal driving when you go WOT - wide open throttle - the vac is supposed to drop to zero quickly and then you get good upshifts. (Good thing to check when you tee in the Mityvac; just put it in neutral and give it some gas; vac should go from say 15 to zero immediately.) Vac comes back when you let off the throttle and come to a stop. So vac is needed only for downshifts. My recollection is that when I disconnected the vac, the downshifts at a stop sign were like a slide hammer, really jolting.

As I remember you only adjust the vac modulator a few clicks either way. They say the new ones which do not have a black cap are not supposed to have the cap removed and then put back on but I did mine several times; seems to work fine. The original ones with the black cap supposedly were the only ones with a cap that could be removed, adjusted, and then snapped back on. Opinions vary about that.

However, Kerry is the expert. Listen to him.