[Tannaton]

As chap above said - unfortunately it really needs to be diagnosed by reading live data as it is showing symptoms. If it's not fuel pressure then its likely to be electrical.

Given it's a diesel engine, fuel pressure could be an issue (hence the dealer replacing the regulator) but I would expect that to cause fluctuations in engine power rather than stuttering?

A single injector could cause this if it was jamming open - again you can trace this with VIDA as you can disable injectors individually. If this is the case, it could be quietly clogging your DPF as well.

I would also check all electrical earths are sound in the engine bay, around the ECU, and the battery terminals.