[VetteVet]

This most often points to a voltage regulator issue. Of course it's in the alternator, before you buy a new alternator try checking all the connections to the alternator including the plug and the wire(s) in it.

With a fully charged battery I would disconnect the alternator wiring and start the car to see if the flickering happens. This would isolate the alternator from the system as a cause.
You most likely will see some codes relating to no charging but they can be reset.