May be time to check the fuel pump - it can go bad, or literally fall out of it holster inside the tank and lose pressure because the fitting it uses to pump to the fuel rail is the only thing holding it in place!
Had a GDI system with low-fuel pressure - even changed the module that regulates the pressure until the tank got opened up and there it sat - laying in the bottom of the tank out of the holder bracket. So you had to - pour - siphon out the fuel - pull out the pump and reinstall a new one. All set...