I'm wanting to get the ZZP Downpipe for 2005 GTP, and I want to make sure I get everything that I need. There are 3 options to choose from. 3 inches, 2.5 inches, and 3 inches with 3 inch outlet. If I'm attaching this to everything else stock, which one do I select? Do I need gaskets for each end? And then there's mention of the O2 sensor extension. Do I need this as well?
I'm starting there, but will most likely get the Plog also at a later date.
Is there anything else that I'm forgetting?