have you tried looking at your voltage regulator? mine went down just as you describe back in 97, in fact I would just park my car on an incline when ever possible cause I could find a replacement at the time (didn't really have access to the net) so that was a main reason for having it sit for so long. I had my starter tested the new and old generators and at first the battery that was in the car when I bought it was bad, but then I put a new one in and it did the same thing. so that was when I test the new generator, and that passed as well, after that we figured it was the VR but since it would at least push start that due to the availability of the part at the time I just didn't do anything about it.