[bigchillcar]

Ditto to what KurtV said.

Do you know if your alternator has an internal or the external voltage regulator? This is supposed to regulate at 13.5-14.5, if memory serves me. If you have the external, they're not too expensive to replace and quite easy to remove, should be just forward of the ignition box with two wires. The internal one will require the infamous alternator removal procedure. This job takes me about 4 hours, but a good shop would do it in two. On the other hand, if its the alternator you suspect, if you can get it out it can be bench checked by an alternator repair shop...and maybe repaired.

What is happening during all of this with your generator light? Is it coming on? It should be coming on to alert you that the system voltage is dropping and may be running on battery only.
Ryan