severe voltage drop at low RPM

Heyo I've had my 3kgt for about a year now, and for the past 6 months or so, when i start it up the voltage runs at an appropriate 14.4 volts, but as the engine warms up (may be unrelated to the heat tho, dunno) the voltage becomes reliant on the RPM, at idle it will drop down to battery level (12v or so) and at cruising it sits at low 13. if i turn on my headlights the voltage drops about 1v, and the turn signals pull it down a universal pulsating 3v, even dropping down below 12.2v in idle.

it wouldn't bug me all that much, except that i have an aftermarket stereo/speakers that are suffering because of it.

what could be causing this? and if it is the alternator, does anyone know any good resources for aftermarket high output alts?

iits gotta be the alternater