In the interest of deferred maintenance, I replaced the fuel filter, fuel pressure relay and TPS. All were original and corroded. The TPS in particular was brittle and the screws required an extractor.
After each part, I restarted to test. Same result, although at one point just after hitting the TPS screws with a small hammer to loosen, the truck did start and run for a minute. WTH. It failed afterwards but seemed to run a little bit longer after the TPS.
After replacing the 3 parts, noting the fuel in the fuel filter was not horrible (I've seen much worse), the truck still started and instantly stalled. Grrrrr.
I removed the air intake hose again, between the MAF sensor and the split into two hoses that leads to the intake. I was going to spray a little MAF cleaner just out of frustration. No rationale here, but I decided to check the PCV valve (it seemed fine) and started once again. It started and ran relatively fine. I removed the air filter cover, inspected the box and found a clean filter and no evidence of rats. I let it run, I revved it up, I put it in gear wtih the brake on and floored it. All good.
So, MAF sensor gone bad? Would taking it out of the air flow path allow the truck to run? I'm definitely confused now.