I recently had a P0401 code show up on my 99 GTP. I pulled the EGR, cleaned it and put it back in and a couple days later the code was back. I next went ahead and replaced the EGR with a new GM one and that worked for about a week and then the code was back again. Last night I pulled the metal flex tube from the EGR to the intake and cleaned it as well as the EGR port, but they weren't plugged or really that dirty so my guess is the issue will come back, what else do I need to look into on this?