hint to get some extra horsepower you may have lost. check your a pipe where it makes the 90 degree bend and goes over the oil pan. they all get scraped it's just the design, but it's possible for that pipe to get smashed and look fine from directly underneath. I just replaced the whole pipe because the flex coupling was leaking and found out that it was smashed to only 1 inch thick, I thought it was just scraped like most of them are, and what a difference once it was replaced. the very design of this pipe makes it venerable to road debris and other things like parking space dividers etc. it's very easy to damage it and cause a big exaust restriction. also a money saving tip on this pipe, it costs like 150 bucks at advance but if you can find one that just has a leaking flex coupling, the couplings are available at muffler shops. I found one at the junkyard that was fine except for the flex coupling and the total cost of parts and labor was like 50 bucks. the junkyard part was free.