I made it 700 on the first reset until it occurred again. I think you are right about the gaskets. I have long tube headers to AAM 2.5 true dual and HFCS so I think maybe the dealership loosed the connection past the HFC to re hang the exhaust and didnt tighten it all the way. For now though do the video game cheat to reset the code!
https://www.youtube.com/watch?v=95WszTnphPI