Conclusion -

Just replaced the housing.... bike now shifts like new.

So I don't know how much of the other things I did helped, but apparently the front housing was the main culprit, if not the exclusive culprit.

Funny how that works... cable looked perfectly good to me, cable ran through it like buttery silkness when disconnected... but the inside liner must have been rubbed out or something, 'cause installed and under tension, it was hanging me up.

Thanks for help, gentlemen.