Thanks RLSH700 for the information about the overdrive transmissions and how they can effect final drive ratios. But, I'm an old timer and in my drag racing days you just changed rear gears and knew what would happen. Could you show me the math you used to figure out that final ratio for the Challenger? If the overdrive changed the Challenger's final ratio then the Truck's ratio should have changed too. What would its final drive ratio be? Please show the math for that too. Maybe I can learn something here.