What year is your ACE? Or more specifically, does it have the 5 or 6 speed transmission? I bought the 5 Star for my 5 speed coach and it did help with the shift points, reducing the downshift for every little hill. Wasnít a magic cure all though. I did not find any advantage for the engine performance. I subsequently bought a newer coach of similar size to yours with the 6 speed transmission and I do not plan to purchase the tuner for it.