Update: had to leave the truck's battery on a trickle charger the last couple days, so when I went to go reinstall the battery today I decided to take advantage of the strangely good weather here in Bay City and start it up.
After it was running I putzed around swinging a wrench at the ECM to see if I could trigger anything, wiggled wires, etc. Nothing happened until after a few minutes the truck's idle shot up to about 1100 RPM judging by the sound. I ran around to stab the throttle a few times and that was it, it stalled, wouldn't start with the relay in, etc... I made a mad dash for my OBD-II scanner.
The reason I am so stuck on these, is it would explain your symptoms rather well..... If this ain't it, we can move on to something else.
After getting the truck going lacking-fuel-relay, the live data on the scanner showed -40C for coolant temp. I ran to get the other of my two name-brand repair manuals, I found a distinction between the Engine Coolant Temp sensor and the dash gauge sending unit. You were indeed correct HeyYou.
I found the other sensor, the two-wire one just behind the A/C compressor that apparently goes to the ECM. Here's the strange part: The sensor was completely snapped in half, with one half connected to the wiring harness looking like a rusted thermocouple just flapping in the breeze, and the other half screwed in to the block looking like little more than a bolt with some corrosion on it. Strange considering the issue was rather intermittent, as I don't suppose the right speed bump would magically flop the sensor bits back together to function.. this sensor was obviously and completely inoperable.
21 bucks at O'Reilly auto parts later I have seemingly reliable coolant temp data to the ECM. I have not driven the truck anywhere yet (worst case scenario, being stranded in 15 degree weather isn't fun). However it did stay running in the drive way for the better part of an hour and a half or two while I cleaned the truck out and addressed some other zip-tie-and-duct-tape issues.
Idle stayed at a steady 600 RPM, and with occasional stabs at the throttle giving no hesitation or sputter except for an uncomfortable dip down to about 350-400 RPM before returning to Idle.
I cleared the codes just after the sensor replacement and the only other code to come up was a "lean mix - bank limit". Perhaps a good thing in light of our theories?
Regardless I'm still skeptical of future test drives considering the nature of the condition I found the sensor in, as I mentioned earlier.