You have to be careful what exhausts you put onto a sportivo. Maybe the exhaust you have is too free flowing, so not enough back pressure, that is why down low you may be losing power. Most recommended exhausts are Remus and CES, not sure about Apexi N1 or Magnaflow. They are both proven to gain for the 2zzge. I heard there is a TRD muffler also availble for our cars, but no one seems to have it yet.