The 2 things that I would start with are.
1. Fuel tank vent line possibly blocked. This would not allow the ambient air into the tank thus creating a vacuum effect inside the tank. Remove the fill cap and listen for it to suck air into it to equalize the internal vacuum. If so, follow vent tube and clear it of the blockage.
2. Remove fuel pump from tank. Inspect the pump assembly and pick up filter. It may need cleaning or replaced. Possible rebuild or replacement of pump as well. With 55psi, it’s already low and out of spec.