I had a similar experience. I replaced the right engine wear ring and impeller on my 2009 Challenger se, and that (right) engine was turning less rpm's at full throttle than the left side (all low speeds seemed to match). The boat was just as fast, or just a hair faster than before any work was done so, in my mind, thought it was doing so because it was 'more efficient' than the older left wear ring. I have never seen a sync light, and the difference is around 500 rpm. I bought the boat used so theres a lot of unknowns. I'd like to see if anyone else has some imput on this.