4.3 alternator low voltage but charging
 

Hi everyone, I am currently reading a hair over 12 at 1200rpm and even when i rev the engine more it doesn't really go any higher. I've been meaning to read the voltage directly off the battery but keep forgetting to bring my volt meter. I know the alt is charging because I loosened the belt a tad a used my trim pump and i could hear the belt start to slip and rpms go down. Now if the battery voltage is the same as up by the dash what could be causing the issue? Does this sound like a faulty volt regulator? Also my gauges sometimes bounce around a bit. Im guessing this has to do with low voltage? Thanks!!