I have replaced the egr valve 2 times in the last 2 months. Still get the dtc p0404. I have checked the egr tube for clogs. No clogs. What else could this be? COuld it be the intake gaskets? How could I check this? The truck runs perfect no matter what. Truck has 94k on it now. Does anyone know if this truck has a DPFE sensor? Please help!