rebuilt alt and new battery...still problems

[missionx96x]

Ok I have a fresh rebuilt alternator a month old and a brand new Optima yellow top battery 2 weeks old. I drove the car today after bein down for a week and I notice that it starts up nice at 14v then as im driving it goes down to 13 then 12.5 then stays at 12 and i come home its still at 12volts. I dont understand whats wrong. What could be the problem here? Is there any chance I got a bad rebuild? Could my wiring be bad or something?

 

[missionx96x]

Whats the difference between 1g and 2g alternators? I have a 97 gst with a 6 bolt swap. You think I most likely have the 2g alternator because it would be a pain to switch to the 1g?

 

[importboost]

If the swap was done correctly you should have a 2g alt. Where did you buy your rebuilt alt from? i know some of my friends have had bad experiences with rebuilts from Advance Auto Parts.