69 charger low battery voltage

Hello!

I have hahavebear of a time trying to figure out why my battery voltage won't get past 13V. For reference I have a 440 with electric fans and an electric water pump. Whenever I drive my voltage will be anywhere between 12 and 13 volts with it slowly dipping below when I'm at an idle at a stop light. I ran some tests today and I get
*14/15V at idle coming from the alternator's battery terminal.
*10/11V at both the alt and VR on the green wire connecting the two
*12V on the IGN side of the VR (I have the earlier style VR and points distributor)
*when I was driving, anything I turned on or off (water pump, fans, headlights) would have an effect on my volt meter. i briefly turned everything off while driving and my volt meter shot to a little above 13V and my Ammeter jumped more towards the center (its usually pegged to the charging side when off idle). Does that mean my alternator isn't strong enough? It is a 4 month old remanned Ultima 55 amp squareback alternator. Any help would be appreciated as I am stumped at this point.

Author: Rchab