You will probably not like what I am going to tell you: chances are that, regardless how much effort you will put into get a new map (a weekend app.), you will never get the same power as with the stock muffler. Sounds like shit, but offers best performance.
If you are still using the stock inner airbox cover, get a perforated one, as sold 2006 and later. This will help more than a K&N.
"It is often said that before you die your life passes before your eyes. It is in fact true. It's called living."Terry Pratchett