the little screens above the fuel injectors are probably worth an inspection
which also allows you to look for tip deposits too

you are correct to suspect the very rusty engine
perhaps someone here on the forum would volunteer to run a Carfax
for you

 

Just to follow up in case there is anyone with a similar problem searching the archives for answers, the plug wire TSB seems to have cured all my problems. My truck had every single symptom listed in the TSB, and re-routing the wires cured the problem. I don't know why the problem started mysteriously without any other changes, but the wiring was indeed the problem.

Just an FYI for anyone trying to figure out why their truck is running like crap.