I know you know this, but I am going through the logic .............
The pressure regulator is the only part that lowers and keeps the pressure constant, provided the pump has the volume and pressure to be higher than the regulator setting.
"If" that is correct, the only other cause for HIGH fuel pressure are "restrictions" to the inlet port of the regulator, or, regulator outlet to the tank.
This includes hoses and lines. There have been sightings of rubber hoses failing internally, without any visible outside indication , as well as having the hoses hooked up incorrectly.