So I spent several hours rooting around my harness and don't have much to show for it. This is my first real attempt at troubleshooting a wiring issue, so if I come across as not knowing what the hell I'm talking about it's not a ruse.
I dug up a wiring diagram, and found a circuit (BLK/RED) that's shared between the TPS, CLT, IAT, old O2 sensor, Fuel tank pressure, and EGR boost sensor. This seems like the culprit, because I've now discovered that my IAT is also messed up (stuck reading at 70*).
I checked between all the connectors under the hood for blk/red continuity, they seem fine. No obvious breaks in the harness, I took the top chamber off the intake manifold and looked around in there too. Re-cleaned my grounds, they seem fine. I haven't crawled under and checked the fuel tank pressure connector yet.
I removed all the EGR crap a while ago, and put block-off plates on the back of the squaretop when I installed it. Also, as you can see in the below pic, I capped the tank purge line because I had seen other people on a returnless system do this without issues. With the 100* weather last weekend when my sensors went kaput, do you think I had excessive tank pressure or something related to EGR removal that could have caused a short in this circuit?
That's it for now. Wiring issues are soul-destroying so I had to come inside and pet cats.