CM2230 Unstable fuel pressure

[Aleeex]

My uncle is is chasing an issue and cannot find the source.


He has been getting fault codes for unstable fuel pressure, fuel pressure below normal, and above normal.


Truck already has about 700k miles.. Believe it or not but an inframe has been performed at 450k.


Fuel pump has been updated by the dealer.. High pressure relief valve has been replaced.. And I think he has tried replacing 2 injectors.


When he does the fuel pressure test, says it holds fine (followed rawzes youtube vid)


Any ideas on what can be done?