Shane95Z28

Hey guys need some help. I got a 96 camaro 3.8 just replaced the alternator and the battery. Voltage was normal then when I drove it around the voltage droped down to the first red bar and stayed. I tested the alternator and it was no good however when I put the other new one in its doing the same thing after driving a bit the voltage drops back to the red line and stays.It seems like something is causeing the alternator to go bad rather quickly Any idea's ?????