Yea def get a tune that may help, another thing you might wanna try is fuel injector cleaner, we find it very useful for gas mileage not sure on the brand tho, try using Shell gas only.
As far as tbe, I have a Trust Ti with aftermarket cat on my ride and it has a low growl to it from what my peers say when they hear it, they stopped makin them so u can find some good prices out there got mine for almost half of what they retail. Another deep low exhaust is the Blitz Nur-Spec.

 

check out rocket rally if you don't want to cross the border.