So, update to things. Parts truck has arrived, 99 Mountaineer, 124xxx miles, 5.0 V8 AWD, and it's rotted, bad, and won't start still, won't even attempt such a feat. Meanwhile, I've done some work to this truck. It's turned 272K miles, abiding some collective issues, so I did some work to it today. First, fuel filter. I'll start by saying I forgot it when I bought it, and didn't remember until this week. No clue how long it'd been in there, but what caused my remembering is a lack of power, bad hesitation, and cranking a long time to start. As for how bad it actually was, releasing the pressure at the rail doesn't release the pressure before the filter if it's clogged. Glad I was wearing glasses.
I also took out the Bosch plugs it's had since 257K miles, since they were used out a motor for a project, and put in Autolites. The Bosch plugs were shot, they had a ton of white crusty buildup on them (Lean?). One of the two made an amazing difference in the truck, it's strong now, no hesitation, no vibrations like before, nothing, dead smooth driving.
*Edit* I can't find anything in the paperwork it came with or the records on MyCarfax to suggest a fuel filter was ever changed. Filter is presumed OEM like the front suspension and belt when I bought it. It's so clogged you can't even blow through it, what ran out looks like chocolate milk.