StevieTD5

Going out of my mind Defender 90 TD5 year 2000 Ongoing problem with engine fault, Had to replace Cylinder Head and its not ran right since. Felt sluggish in every gear and when I went over 60 it cut out! Back to the garage! replaced all hoses and pipes, replaced fuel pump, sent ECU away to be checked (came back with no fault). Now it wont start. Thinking it might be the injectors.... when replacing the head, is there a set process that should be followed?? Any ideas?? Thanks Steve