I got an 05 gt and was wondering what’s the best long tube headers and off-road x pipe setup?

 

Have you searched the sub-forums, if not? select the search tab by clicking it and then type in the drop down menu what type of exhaust your interested in. There you'll find plenty of threads that cover exhaust systems.

 

Yeah, like he said, there is no one "best" but there are lots of options and trade-offs and searching through the existing threads is probably about the best way to get a feel for that

one quick comment: remember "off road" means "illegal for use on public roads in the USA" and personally I would not mess with it, you might get away with it but I'd rather keep my car legal