Alternator gauge flutters

My Alt gauge is fluttering back & forth at mild cruise speed. I flutters between 1/4 and 3/4 full charge approximately. It is a 73 Dart Stock Charging system. I did do a search but didn't find anything for "Fluttering". Just hoping for a quick point in the right direction. My ground tests good at VR.
Thanks in advance for any advice. I really appreciate all the help I get here:prayer:
I am still going to do the MAD upgrade. Maybe now is the time to do it?