[VetteVet]

Your readings indicate that the alternator is charging OK so now you have to find out if you have a drain on the battery. Since you have a meter, take the negative terminal off the battery and connect the meter leads between the negative post and the negative cable with the meter on amps. 10 amps is the setting to use.

Make sure there are no loads on the system, lights, radio, memorys, etc.
You should read not more than .004 milliamps. Or .4 amps .002 would be best but you probably wouldn't kill the battery at .4.

If you get more than that you'll have to find the drain by isolating the circuits.
It's a key off drain so it shouldn't be hard to find. The alternator is the first culprit. Take the reading and post back and we'll go from there.