Vue '06 3.5L All lights flickering. Battery and Alt replaced 4 months ago

[akshat]

The alternator died on this 2006 Vue 3.5L around 4.5 months ago. It took the battery with it, and so I had both replaced.

I didn't have my tools at the time, so the alternator was done by a decent mechanic (though they said they used an O'Reilly alternator — I feel like I've heard talks about auto part store alternators being finnicky with the Vue). The repair looked like a decent job, and the car battery was being charged so I had no complaints.

The battery I replaced myself with a Walmart battery to spec. I got the felt pads, cleaned the terminals and tightened to spec with a torque wrench and added battery terminal grease. I've looked at the connection and it is still tight, hence I find it unlikely that the battery is the problem.

The issue I've recently noticed is that when the engine is turned on the lights on the dashboard, headlights, and interior lights are all flickering. I installed an aftermarket touchscreen stereo but it does not flicker (I believe it has some circuit to prevent voltage fluctuations to hinder performance).

https://youtu.be/I9PIoP4HMb4?t=59 This video is exactly what the interior and exterior lights of my car look light, only when the engine is turned on. With acc power, everything operates normally.

What I've currently tested:
1. Visual inspection of terminals + connections
=> Terminals on battery and alt look good.
2. Test alternator by checking battery voltage with engine running
=> Battery reads 14.3-14.5 V with alternator running.

As I haven't had much time these are the tests I still need to perform:
1. Check battery voltage at rest
2. Check engine ground connections (test resistance < 5ohms) starting with battery, alternator, other parts of engine.
3. Clean and double check alternator connections (Just in case)
4. Check DTC codes

If none of this works I'll head back the the mechanic and ask them to take a look, but if there's a relatively easy fix I'd like to try that first. A part of me thinks that it might be the alternator they used. Initially I bought an Denso 210-0546 remanufactured alternator but it ended up being broken on arrival so the mechanic just ordered one from O'Reilly and replaced it. I've read things about Vue's not working in the cold with some alternators that have bad voltage regulators/are rated for 130amps instead of 110amps. Since it is getting cold where I live, I have a feeling this could be the issue, but I want to really get a good look at issue and give my mechanic the benefit of the doubt that they installed a decent alternator.

If anyone has any advice or tips for this issue, I'd love to hear them.

Edit to add:
I just found this video: https://youtu.be/iprTa84MeFc and the flashing looks like a much more exaggerated version of my situation (For my actual situation you can see the first video). Since it has only just started getting cold and currently around 10C (50F) where I live, maybe this is indicative of what is to come when it gets colder. The video specifies that the issue is a bad voltage regulator on an aftermarket alternator, and so it's looking more likely that this is my issue as well.