Can't Eliminate P1407 code
 

I have a '95 3.8L that is displaying P1407 code. I have changed the EGR valve, DPFE sensor, EGR vacuum regulator, and a cracked hose to the DPFE. But it still continues to display a P1407 after I clear the codes. I can drive the car less than 40 miles before the 'idiot light' comes back on with the same DTC. What else can I test for???? Desperate!