I have ls 3.9 the p0402 code keeps haunting me. I have replaced the left bank 02 sensors, egr valve and the egr pressure sensor. The car run great with no hesitation so I don't think its a cat. Each time I have replaced a component I have disconnect my battery to reset the code, and it keeps coming back.
First, I would verify both vacuum and exhaust are present at the egr valve. If one is missing, it needs to be repaired.
Did you mean the dpfe sensor? This is a common failure.
Does the solenoid work? And if it does, does it pass vacuum and open the valve?
There is a lot to this system and you need some help from a shop. Throwing parts at it is expensive and most likely wrong.