Hi, I have a 6 cyl 2004 Envoy XL w/ 145k on it. Around 50k, I began to see the voltmeter fluctuating between 12 - 14. I saw the lamps dip, and heard the heat / AC fan slow when it happened. No biggie really. Recently, I have noticed the lamps fluctuate back and forth very quickly (1/8-1/2...