Disco 2 td5 running issue

hi everyone im new to this site so if anyone on here can help me out with the running issues i am having with my disco id really appreciate it. it is a disco 2 td5 2004 purchased it and it was working fine for a few weeks then started to struggle to start sounded like it had air in the fuel system so had to do the air bleed procedure. then it would finally start so i came on here to look and found a few things it could of been and started changing parts but it still havnt fixed the problem if anything its gone worst over time so far i have replaced
) injector seals and copper washers
)injector harness
)high pressure fuel regulator
)fuel filter and fuel filter houseing
)fuel pump in the tank
also had the ecu checked incase there was any issues with that. Anyone that has simular problems that could point me in the right direction would be great thanks . Ben