Thanks for the suggestions. I'll have the guide pully, cable housings (and friction), and hanger alignment scrutinised by the shop. I still may swap out to a slightly longer chain to better accommodate the 28t rear cog without so much b-screw tension.
The cables are practically new because the old one frayed under the shifter hood and snapped a couple weeks ago. The new one is somewhere between 250 and 350 miles, but that's still fresh.