When did you get the gs setup? I did hear the early ones were a bit off in terms of fitment and quality, but have improved since then. The main issue being the dump tube clearance on the axle.
My experience with gs has been nothing but good, including fitment.
Also, turmic, I can't comment on the the mod being worth it, but everybody I talk to ranks it as one of their best mods. From what I hear gains are all but minimal, and moving the whole powerband to the left while still having near full-boost all the way to redline is pretty sweet. Granted my injectors may be able to hold me back if we can push a good amount of boost to 7k rpm's. Add in the fact that it will only add more sound once I'm pushing over 14.5 or so psi, I'm not worried about it getting annoying.
I also might be able to get some used parts from a guy and do the whole setup for about 400, including thermal coating and heat wrapping the pipe. That would make it much more cost effective.