I have one of those for my next bike. I've read that it needs more back pressure. I think you, DieselTech said about 5/8 is about right?
I did a mod on a stock one as my glass pack one lost it's quieting effect, but I need more pictures to show what I did. The short version is, cut it open, remove the stock outlet pipe, add 1/2 inch copper in it's place{all I could find). Slot out the baffle plates to fit the new pipe and cut the baffle plates exhaust holes wider. Braze the new pipe in place.
I know this is a lame explanation but it will have to due for now.