Charging System Failure 2005 Z71

[JAG66]

Started my 2005 Z71 to leave work, "charging system failure" displayed. Lights dimming, wipers getting slower, gauges stop working as volts gradually dropping from 14 to 9. Truck finally stops running at stop sign. All this happened within about 8 miles of driving.
My first thoughts are alternator.
After about 20 minutes tried to start, and click, click sound, like a dead battery.
Receive a jump start and drive 1 block to Advance Auto. Gauge showing 14 volts.
Charging system check performed at Advance and battery and alternator all good.
Turn off truck, truck starts right up and holding steady 14 volts.
Drive home with no charging system issues. But no confidence in driving to work tomorrow.

Any ideas? Anyone had this "charging system failure"? What else should I look for?

Thanks, Jeff