Just to give this thread an ending, I never figured out WHY any of that happened... All attempts to measure the pressure were a failure (the fuel pressure gauges would either explode, or be unreadable because the fuel pump doesn't supply a constant pressure)....

I pulled the tank out(and pressure washed it clean), replaced all fuel lines, but they were all clean and had no gunk. I am guessing something was stuck somewhere IN the pump in such a way that it wasn't getting pressure, but one day all of a sudden for no good reason, it just started working right again. I wish I could say I know why, but I still don't have a clue