Weird overcharging issue

In addition to above, as I eluded to earlier, you want to try to determine if it is working "somewhat normally" and then suddenly overcharging, or is it dropping off, allowing the battery to go down some, and then suddenly "kicking back in?"

Some other things.......

Remove VR, scrape around the mounting and remount. Make CERTAIN it is grounded, and mounted tight

Remove and inspect the VR connector. "Work" it in and out several times to scrub the terminals clean and to "feel" for tightness

Might be brushes are worn, sticky, dirty, cutting in / out

'Rig' a voltmeter in the car so you can monitor voltage, both when seemingly normal and during the "high" spike.

Read the MAD article, even if you don't do that modification. It gives a great overview of how the system works and problems inherent in these girls

http://www.madelectrical.com/electricaltech/amp-gauges.shtml

Check the belt condition and tightness

I would remove the bulkhead connector plug sections and inspect them after reading the article above