Help! Baffled by charging issue

[RenaissanceMan]

I'm having some issue where I'm getting intermittent alternator operation, or something similar. Occasionally, battery light will flicker and by monitoring the voltage using Torque Pro, I'm able to confirm that voltage at the battery is under 12 volts and steadily dropping for a while before suddenly jumping back up to 14 volts. Yesterday I almost got stranded because on my way home system was not charging and I went from 11 volts all the way down to nine volts while traveling on the highway, and then I had all sorts of warnings and system failures occur. I got off at an early exit thinking that it would be safer to get towed from there, but as soon as I got off the highway and came to a stop, voltage jumped back up to 14 volts and charged the battery again. I was sure that the problem was either a failing alternator or ignition switch, but I replaced the ignition switch with a spare to no avail, and the alternator tested fine three times in a row at the auto parts store just now. What the heck could be going on? Will a failing alternator display these intermittent symptoms? I've never had one do this before.

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