Alternator Problem or Not?

I have a problem with a '94 3000GT DOH Automatic , the battery would drain if parked over night and needed to be jumped. once started the car would run fine and the battery would stay charged as long as it did not sit idle for too long. The Voltage gauge would read around 12 until the lights, radio, and AC cam on, then it would slowly drop. once the car warmed up it would idle around 600 rpms. I was told the alternator was bad and a new one would fix these problems. The alternator was replaced (new, not a refurbish) and this solved the problem of it loosing its charge if left over night or even days. however, it only solved this one problem . Also, activating the turn signal causes the voltage needle to tick up and down in sync with turn lamps(not sure if this is normal). Are any of these problems related and does anyone have any ideas on what should be the next course of action?

Voltage drops on all 3s's. The voltage gauge also flickers with the turn signal on all 3s's.