At a cold start voltage stays at 14.5volts . After it warms up it drops to 12v at idle and fluctuating to 14v. Lights dim down until I give it gas then voltage pops back up. While driving it drops to 12v when the trans shifts gears into a higher gear. Sitting at a red light it just fluctuates from 14.5v to 12v very quickly. With no loads on motor, no ac , no heat, wipers or radio. It’s getting pretty bad to where I can’t drive it. I changed the alternator several times, belt, tensioner, positive and ground cables, alternator plug, battery several times, new pcm, IAC valve, tps. Still no change. And yes I only use FoMoCo parts

any help would be appreciated