HI, I have a 125xxx mile 2000 f150 5.4

when sitting 1-2.5 hours, she just cranks and cranks and finally stutters, hesitates and starts.

In a recent thread, I stated that I just changed the plugs and it runs better but hasn't fixed problem.

checked fuel pressure tonight, it was at like 5 psi after sitting a while and soon as I cranked it, the psi went to 40 yet it still took some cranking to start.

I am thinking the crank sensor might not be signaling injectors to fire, fuel pump is weak or relay is bad. I tapped the tank a bunch but pressure didn't come up until cranked.

any advice, thank you so much