That muffler is fairly long. Actually has a few staging points. It is likely pre-staging up on the muffler real early in the throttle range (40-50% throttle), then transitions up to the top end near 85-90% power. The sleeve is not agressively timed. So there is likely no real noticable rpm step. More of just a torque curve shift rather than a giant rpm jump. I find that with some of the bigger engines. Once it the air, it should stage just a bit more up on the pipe into the more useful power range.

Im glad its working well for you