87 4000cs Alternator failure? (Nolan Gilliam) rukshawmaster at msn.com

[Nolan Gilliam]

So it got really cold this week up in the Seattle area. Last night I noticed 
my stereo cutting out. The voltage meter in the center console was 
displaying volts around 8 which is pretty low. Battery warning light came on 
as well and my tachometer was bouncing around like crazy. This was all while 
I was driving too. So this morning I start the car. She turns over 
hesitantly and the tach is bouncing around and the idle has a mind of its 
own as well...  I keep the revs around 3k for for a good few minutes to try 
and warm the car up. I let her back down to an idle and she stalls out. 
Tried to turn her over and the battery is dead. So i get a new battery, pop 
it in and she starts up fine. No electrical failures at all. Drive it to my 
parents house, watch Seattle loose to Chicago  Come back home and then leave 
for work. While I'm driving i notice the volts output is really low again 
and the stereo starts to cut in and out. So obviously its not a bad 
battery...Does this sound like an alternator issue? Faulty ground?