I recently went from 4.56 to 4.10 with a 28. My car is slower, 124 MPH. In my case The motor was losing steam with the 4.56 and showing very little converter slip because of it. I changed a few things with the 4.10 setup, looser converter, and 727 to 904. The car picked up at every increment, execpt mph. My finish line RPM only changed 200 or so due to converter slip.