Tuff 150 amp alternator

Good evening everyone, I have a tuff 150 amp alternator installed on my Duster. I have converted my charging system to the Mad Electrical wiring set up. So my question is does anyone have an opinion on why my volt meter starts oscillating above 1k rpm. When I add more rpm’s I notice that my lights start to pulse in sync with the voltmeter. I have checked the connections, and verified 12 volts to the alternator. Replaced the voltage regulator. Any thoughts on this would be appreciated. Thanks