transit connect 75tddi no power need help

[adamh84]

as above i have a transit connect its annoyingly slow ive had a new fuel pump head skim and gasket heater plugs ive swapped the 2 air temp sensors map sensor and the other sensor near the map on the bulk head... it makes a weird sound around 2k rpm it has always been slow and the other month lost compression on the 3rd cylinder so had top end rebuild but i dont think they replaced the injector which might still be faulty anyway is any1 around the stockport/manchester area able to diagnose the problem im guessing injectors?