Seriously Need Help

Ok I have 64 cuda 273. Notice amp meter about 3/4 charge and bouncing with blinker and going below strait up at idle. Wow it acts like a generator does.
Headlights even dim then brighten slightly at acceleration ( back and forth). Tried two different new voltage regulators with no avail, Alternator putting out 40 amps,
tried a different one with no avail. By passed the amp meter, that’s not the problem. Electrical system holding between 13.5 and 14 volts. This isn’t normal is it?
Battery is good, checked all grounds and connections. I am at a loss.
Garry