I went with an OD on my sm420 and love it. 75mph @ 2500rpm in 4th over. Stopping the truck IS a problem even though my drums are in good shape. I almost had an accident driving to Seattle from Portland a few months ago. I thought I had left plenty of room in front of me, but when it came time for a sudden unexpected slowdown, there really wasn't. The truck got sideways and I avoided a collision with a truck and a guardrail by about an inch. Needless to say, there are disc brakes in my near future.
