2001 computer problems?

I have 2001 grand caravan, 2wd, 3.3 flex fuel, 118,000mi. It all started with the a/c going out and running ragged. I ran the codes and it came up throttle position sensor, replaced. I used a connector lube on this and the Idle Air Motor in the throttle body. This made the connectors rather easy to slide on and off, but it was running fine. It didn't fix air so I took it to the shop where they replaced a/c High Pressure Switch. It ran great for about 2 days then check engine light came on. I took it to the shop, they said it was ECM, so I replaced with a rebuilt one. I installed the new one and I am still having same problems. I'm getting p122, p123, p107, p106, p1478, p1496, p1648, p118. All pertaining to voltage. So I took it to Autozone and they tested battery and alt. Both were good, battery had a low charge. So I charged it with no improvement. The symptoms are I will start it up, check engine light comes on, and it begins to tach up and down between 950-2500 rpms. The battery light will come on and it will idle off at about 1500rpms after 30 sec. Of running. While driving it will immedately try to drive off when putting into gear and wants to run about 25 mph WITHOUT ever touching the gas pedal, but with pressing the pedal the engine will start to choke out, trans. Will slip after 40mph or if pedal is pressed to hard. I was told that the rebuilt ECM was also no good but the same symptoms persist. Where do I start now?