I had thought of going from 4.10 to 3.54 in my van but the cost, time and changing the pcm to change mph would not make it worthwhile I'm my opinion. Maybe only change 3-400 rpm and not sure where the optimum efficiency rpm for a 5.9 Magnum is at. Majority of my driving is around 55 mph. 440s can lug, 318s can't.