Well, I think I have determined that the Mean Green alternator has gone soft. Won't provide proper voltage at idle... (the alternator came with the Jeep.)
2005 Red Top Optima holds +/- 12.5v cold with surface charge drained.
Checked auto belt tensioner.
Used multi-meter prior on the battery to start-up, at start-up (no head lights or heat), then with head lights & heat.
Won't hold 12v on the battery under 1200rpm. Drops below 12v at 700-800rpm until about 11.6v when the Check Gauges light comes on.
Revving the rpm's to 2000, it goes up to 14.6 volts.
Worth a trip to NAPA for their test?
FWIW- the Jeep still starts at -19C albeit took a couple of cranks. At -12C, no problem.
Colorado Jeep Club Member #667