Beowolf

I pulled some codes from my truck today and they gave me a P0401 I think (my check engine light has been on for about 1-2 years with that code being thrown all the time so I just clear it) anyways it was a egr insufficient flow detected code but here is the thing my truck has been giving me the same codes for about a year and a half 2 years and I have already replaced the egr valve and the sensor what else can give this code and also what is being restricted in my truck do to this code IE bad gas milage