Electrical issue, fluctuating voltage.

[Xwizit1]

I have a 07 HB, base model, 5spd. I have a 250A Brand X alt, a Kinetik AGM battery. So, when I start my car, my bass remote shows my voltage at the amp, not under the hood.. It usually shows around 13.5V... But, if I turn the wheel, say, to reverse, voltage drastically drops to around 11. Twice the remote said Lo, and the car stalled. While I'm driving and if the voltage stars to drop, i can flick the turn signal, or turn on the blower and that usually brings it back up. I don't know what it is. There are multiple grounds from the aftermarket terminals, and none are corroded.
Thanks in Advance!!
X

[Xwizit1]

I pulled the alternator for the first time in my life ( Thank you, YouTube! lol ) If the alternator is a touch off, of where it was supposed to be, could that possibly be the issue? It's 17 years old, so I know there will be issues. Possibly the PCM?