This data tells all you need to know. If the maximum vacuum seen by the transmission is 6" hg, and the transmission is still flaring, you're basically out of options.

As a final check, disconnect the line to the transmission and plug the supply side and see if the flaring improves. I'd guess that it won't improve.

At that point, you've got no choice but to increase modulator pressure to try to stop the flare.

Chasing a non-functional VCV is not going to affect your flare in any way. In fact, if the VCV was functional, the vacuum to the trans would range from 12 to 0 and the flaring would be much worse.