NEW alternator from NAPA seems to have fixed the electrical problem(!). It read over 14V on initial check, as I would expect. The connector snapped in better than it did on the (chain store...) reman replacement I tried first.
That one tested good when I took it back to them, but I got my $ back anyway. It tipped over on the tailgate after I had it out, and a pea-sized piece of plastic fell out; not a hard enough bump that should have broken anything, imo, so just one more reason for me to think something was wrong with it, despite what their tester showed.
I'll be going to NAPA from now on I'm thinking. Price was only about 11% more than the remanufactured one from the other place, with no core charge on the new one. Idk if that kind of price is common (it was less than the online price; guy on the phone told me they were privately owned and he was quoting more of a wholesale price, Idk why though).