That's defo way to low, check the charge rate first, check at the alternator and the battery.
It sounds as though either the new alt is duff, or you have a major high resistance between alt and battery or battery and fusebox for so much stuff to be affected, batteries can suck a huge amount of power when duff, but you don't mention any starting probs so assume this is not the case.
If necessary temporarily run a seperate new heavy wire from the alt B+ terminal to the battery.
tabetha