Your vehicle should have a returnless fuel system.
Where older systems with a pressure regulator on the fuel rail had a vacuum connection yours has a pulsation dampener with a vacuum line on it and that is all it does.
On the end of your fuel rail should be the pressure sensor,it does sound like that sensor is defective.
Also, in the battery junction box is the fuel pump relay. If that is the problem you must replace the entire junction box as it is not serviceable.
Did you confirm good connections at the inertia switch? Best way is to unplug it and reinstall the plug and make sure you reset it.
Since you manage to get some pressure, I would lean toward the pressure sensor.