I would also not automatically trust the Auto Zone diagnosis. I had Auto Zone diagnose a bad battery (I saw it read "bad"), that was a nearly new battery and a week or so later my same problem developed, that ultimately was a bad diode in the alternator. Different issue, just making the point that their diagnostic tools are not entirely reliable, and I would imagine testing a VR correctly would be way harder than testing a battery (though I can't say I could do any better). Keep us posted on what you find.
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