Mine did the same thing and then I swapped with a spare I had and it fixed it. I'd say get a new regulator and brushes and you're good to go.
Now that I thought about it more, in the end mine was so bad the EGT needle started bouncing around.
In the car I could change how fast the lights pulsed by revving up or down or turning different electrical loads on and off. Then I tested it on a real alternator test stand and it passed with flying colors, I couldn't adjust the load, the machine somehow just made it charge at 15A at 14.7-9v. I never got that high of voltage with it installed.