I just made a big post in the misfire thread in the 2.5 forum. Find it, I explain how to clean the carbon out. It makes a big difference..
The EX gate is bypassing exhaust that would have normaly went through the turbocharger and out the tailpipe. Your tuner must be confused. Most of the gains of the EX gate come from the fact that you reduce the pressure inside your full exhaust system. Typical gains are 10 to 20hp with some higher. It depends on how restrictive your exhaust is and it depends on what the limiting factor is on your setup.