1. The 13.95 V figure you quote at idle for (I assume the alternator) does not "GEL" with the 12+ V figure you get ( I assume [across battery terminals] at idle with no load. (Battery has a solid double ought gage connection to a huge power draw)
2. Per SteveBFL electrical gauges are dependant on steady regulated voltage.
anything else makes the guages "Chicken Bones" thrown on the ground
as a prognostication of what is actually going on , on the other side of the
firewall.
3. "If it ain't electrical , check the rubber O-rings on the inner shaft that the
basket oil filter fits on. If they are "Hard " + NOT FLEXIBLE replace."