I know it isn't cost effective but I would get a TT chip and 60lbs combo. Maybe, borrow from someone else? I really think that will fix it or help a bunch. I didn't go with 80lbs as those are also hard to dial in.
Hot wiring harnesses conduct lower voltages if you want to do some testing on...
Low voltage to fuel pump, battery going out or weak fuel pump are what I would check for.
Factory wiring leaves a lot to be desired.
Slightly depressing gas pedal increases voltage to fuel pump circuit. If that helps, fuel pump is going out.
Maybe go from battery straight to fuel pump test...