After dealing with the AC issue the week before, the following week while my wife was taking my son to school on a rainy morning the windshield wipers just completely stop working! She's able to get it back home. Of course the next day it stops raining, and when I try to diagnose the issue the wipers are working correctly again! Only guess at this point is water intrusion somewhere, but after looking at it from end to end I have no clue. Since it's not happening now, good luck not getting yet another shotgun-style repair at my cost from GMC, so at this point we're waiting for it to rain again and hope it doesn't reappear.