[ImperialCrown]

Welcome to Allpar. 12.2 volts seems low and charging systems can be intermittent. Have the battery terminals been removed and cleaned? Is the negative battery terminal cable ends securely grounded to both the engine and body?
If you have ruled out alternator and regulator, the wiring harness and connectors may be suspect. With the headlamps on and the car at idle, wiggle and move connectors while watching the battery voltage on a meter. If the alternator whine changes or the lights flare and dim, you may have found an 'intermittent' connection. You can also drive with a voltmeter connected to a fuse or lighter socket source for an occasional glance.
Does the ammeter needle move at all? Some of these had bad connections in the dash where they would stay in the middle all the time and not alert you to an under or over charging problem. It should swing + or - at times (like when starting up).

 

[Bob Lincoln]

What is the voltage when idling, and after having sat overnight? Probably this is a bad battery, and the alternator can't keep it propped up. After you fully charge the battery, measure its voltage (should be at least 12.6 to 12.8V), and then run a load test on it. A shop can do it, or you can put the headlights on and it should still be above 12.0V after 2 hours.

 

[Frantz]

Charge could be the problem as it is not much above what the battery alone would be. Still, bad battery is more likely to stall at stops than at speed, makes me think the alternator is the problem if it's a electrical issue. Most cars should be closer to 14v when running if the alternator is good. I wouldn't consider less than 13v acceptable. I ran a chevy 2.5 with completely dead battery for several months using a jump pack to start and just keeping RPM up when I was stopped....