Hi
Look on the driver side of engine-
on the exhaust manifold you will see a smaller tube going to the intake area-(EGR TUBE)
then, off of this tube are 2 even smaller lines-going to a 2"x3" box (DPFE sensor)
check the smaller lines very thouroughly for holes or cracks-
the next likely suspect in (order of pricing ha ha)
Clogged lines-
clogged or sticking egr valve-(it can be cleaned)
finally-the DPFE sensor could be shot-check it closely. It might be blown out or melted-