[Dan Semko]

Frank,
I think that your problem is probably from a bad diode in the alternator which will not reveal itself without a metered check.
I had a similar problem with a new alternator but fortunately the Mike at Dynamics caught the problem before it killed the battery.
Your alternator is probably going to quit which is usually indicated by rapid spiking in either direction,of the amp needle. Before you change the alternator, check the battery terminals first because if they're loose, it will cause the MSD to malfunction and could easily mimic the symptoms you're experiencing. If they're firmly seated, then I'd guess the bad alternator will rear it's ugly head soon.