I was was wondering if this is normal.

13.8 idling in drive no load
13.1 " " headlights on
13.1 " " a/c on fan on high
12.4 " " a/c and headlights on

In park it doesnt drop below 13 volts with everything running including radio all the way up with amp and subs running.
When engine is cold voltage wont drop below 13.8 every thing running.
Alt was replaced less than a year ago I tested the battery yesterday it was weak less than a year old i replaced it today. All my connections are clean. my car idles at about 600 rpms in drive and 750 to 800 in park.

 

Doesn't sound terribly unusual to me.

 

I want my alt to charge while I am sitting, all my fans slow down when I am sitting at a light, my lights dim, turn signal slowly flash. Is this the way our cars were from the factory? Does everyone else have this issue?