Took the bike out on a 50 mile ride today and I'm more certain that the "chainring slippage" and "poor shifting" I've had for the past few months actually was the freehub slipping. Not sure what I could have done it to make it worse this week.

This has been educational -- and glad the LBS was good to me -- but I wish I could've worked on this myself. Just need to find a $^%#* 11 mm allen wrench.