Ok, so someone told me that the cable may not have been "pre-streched" (seated properly at the housing ends). I put the chain in the smallest cog, loosened both barrel adjusters, yanked sideways on the exposed inner cable, and I was able to take up a bunch of slack at the pinch that I couldn't before. Then I reset the indexing, and so far it seems much improved on the stand. Let's hope it holds on the road!