Depends on your budget.. IF your talking low(er) budget I sent my stock muffler to Hawk, installed a K&N Hi flow filter and flashed my ECM with the race map..
The combination of those 3 things really made improvements. I haven't needed to mess with the race map settings but could probably tweak it for a little better performance.
If you have a little more cash to work with you may benefit from a better muffler, but I was on a low budget when looking for the same thing..
I was partially intimidated about flashing the ECM but with the help of a couple How To videos I was able to do it without any issues..
