Alright, here goes. Lots of fixes later, it LOOKS like the issue is gone. Car accelerates fine, hasn't died at a slow/stop in over a week, looks to be running fine. Here's the complete list of what I did before I fixed it, in the order I did it:
-Replaced OEM CKPS with a cheap one off amazon. Fixed the stalling issue but car still wouldn't go over ~3.5k RPM. Both CKPS tested fine on multimeter and still do.
-Pulled and cleaned out in-tank fuel pump. Wasn't a ton in it, but enough that I'm glad I did it.
-Pulled intake side OCV for the CVVT system and found some weird gunk sticking in the center mesh filter. Replaced with a new one. Old OCV still tested good on multimeter and actuated when exposed to 12v
-Found my replacement fuel line had kinked and begun to leak at about the halfway point. Attempted to cut out just that section and splice in new line. Didn't work, leaked worse. Ordered new line and replaced entire line. When I fired it up, the motor began to stumble and sputter until eventually settling into the normal purr. What I think happened here was that the fuel pump had been working overtime to deliver fuel through the old, leaking lines, and without this leak, began to run rich until the ECU compensated. Hasn't happened since.
Now, at this point, I still have the issue where the car will not go over about ~3.5k RPM, begins to stutter and stumble and sometimes eventually die. I take it on a test drive and find a sweet spot where I can cause that stutter without the car dying. I let it ride through this for about 15-20 seconds before I let it back down. At this point it's throwing the codes mentioned earlier and now a new code: P2290 Injector Control Pressure Too Low. I believe that this is due to the vehicle stuttering for so long that it's no longer able to generate enough oil pressure to run the fuel pump. In essence, I believe this code was CAUSED by the issue I'm experiencing, and is not the cause.
I did several things just this afternoon, and now the car is running fine. I can't pinpoint exactly which one fixed it, but sure seems like one of these worked:
-Yesterday evening, poured about 8oz of seafoam into maybe 6 gallons in the tank. Sat about 20h before the test drive
-Replaced cheap CKPS with a new OEM one
-Removed the small plastic cover on the transmission to reveal what I'm pretty sure is the reluctor wheel. Large toothed wheel sitting directly in front of where the CKPS faces. Sprayed the ever-loving crap out of it with PB blaster while the engine was running
-Disconnected battery to reset ECU
So, which one worked? I don't have a clue to be honest, but if you're having the same issue I did, the first part to replace would definitely be the CKPS with an OEM one, assuming you don't have any other codes that would indicate another issue. Thanks again to everyone who made contributions.