How to test alternator only getting 12-13v max

[ericem]

Well, i got my battery replaced a few months ago with a OEM battery. But i replaced my alternator with a non-oem alternator. Now I get 14-14.1v with the lights off. but when i turn on the lights and the max ac, at level 3 fan, i am at 12-12.5v on idle, and at 1-4,000 rpm's max i get is 13.1v. Could this explain my hesistation issue, light dimming at idle, and inconsistent fan speed? What do you think I should do get a OEM alternator? or find another rebuilt, i think the one my dad got doesn't have enough amps.