Problem Solved!! The plastic vacuum line from intake manifold to transmission vacuum modulator was the culprit. Somehow it must have been exposed to a hot manifold or something and it melted closed in about the center of it's length - blocking the vacuum from being able to get to the modulator valve. 4 feet of new vacuum hose about 1 hour labor fixed the problem - no more clanks on upshifts.

Thanks to everyone who responded