2004 Dodge Intrepid Electrical Problems

Electrical problem
2004 Dodge Intrepid 6 cyl Two Wheel Drive Automatic 100k miles

Ok. So my intrepid sat for about a year because the ac didn't work and it was to expensive to fix. Now its out of mothballs because its the best I have. I thought it was having alternator problems. I have a volt meter that plugs ino the cig lighter. It would randomly read low volts and then eventually die. It also randomly kick back on and be fine. I replaced the alternator with a used one. It was a little better for a while but then started up again. When its low volting enough it gets stuck in second gear and the radio shuts off. After that it starts getting hot. It runs hot for a while (probably too long), and then poof. Alternator is back and working and I'm back at full voltage. I'm beginning to think its a computer thing. I'm hooking it up to a battery charger at night to get back and forth to work.