Cleaned at the intake manifold port ?? or the EGR itself ?Its been cleaned not even that long ago. I have a feeling its everything, Motor, cats, egr. Motor probably has over or approaching 300,xxx
NOx is formed by high cylinder combustion chamber temperatures that combines the Nitrogen and Oxygen molecules .. overheating engine, or a non functioning EGR will cause this .. the EGR displaces the oxygen / reduces fuel, so you dont have as much nitrogen / oxygen burning inside the engine to form NOx. The Cats dont really do much for NOx reduction.