I would say to check the charge air cooler and all hoses. Also check the intake hose from the intake to the air compressor. Look on top of the charge air cooler for cracks at the corners (this is a spot that they crack alot of times). Might need to get it pressure tested.
One thing I noticed when they changed the injectors there was carbon deposits in one injector tube,the mechanic cleaned it up and put new injectors with new O rings. Should I be looking for something there?