I recently replaced my alternator in my 02 z-28, when i drive the battery gauge will start in the middle, then slowly make it's way above the red, to slightly in the red. I think having the AC and the radio on effect it more then when they are off, I had a buddy hook up a voltmeter up to it, and my battery was reading like 12.9 and my alternator was reading more. My only real concern is i don't want to be driving on the highway and have eveything power off on me out of nowhere, I checked the battery terminals they look good, and the connection to the alternator seems acceptable also.. any ideas?

 

Today i was driving it around and when i got into the car for the 3rd time it was a little bit harder to start up, it sounds like the alternator is making a hissing sound..... but when it's driving i have no problems... anyone ideas??