Inspecting fuel pump and tank interior
Running down possible problems with fuel supply I needed to take out fuel pump but impossible to drop tank, crossmember and hydraulic jacks would have to be removed. I decided to attempt to do the job from the top, located where I needed to access, lifted carpet, cut foam, particle board, foam insulation, luan plywood, metal sheathing. From drilled pilot hole 1 1/4 inch I could determine where to saw, made a 5x6 inch hole.
Rewired pump to get fuel down as much as possible.
Removing pump found tank to be clean including the pump prefilter, good news but not problem solver. Proved my point that PO spent many hundreds of dollars replacing filters that weren't needed.
Put it back together, more good news, fuel gauge still works, and now I know exactly how much gauge is showing, and that the capacity of the tank maybe 80 gallons but less than 70 is usable. I will always fill by the time it gets to 1/4 tank as fuel is used to cool pump, making the last quarter tank a reserve or emergency fuel.
Now that I have a wire hooked up to fuel pump I will wire it so that I can electrify pump without the things that can stop it, relay, oil pressure switch, computer if needed.
I still have to replace relay and oil pressure switch as nothing wrong was found in my exploration. Only common symptom for fuel shutdown while underway was at least 100 miles and heat. Gasahol might be culprit but haven't found any blogs of recent fuel injected 454's still having problem that old carb models had vapor lock often enough that Chevy sent out warnings and solutions.