Are the coated pistons set to a tighter tolerance as on gassers? I know that certain coatings keep heat in the combustion chamber and away from the skirts so you can run tighter clearances. The main benefit is cold pistons slap and rock causing the rings to round off reducing their sealing ability. Less blow-by keeps the ring grooves (and the oil) cleaner and scuffing down.
I am appalled by how much blow-by my truck huffs out. I think I have more exhaust flow out of the vent and your average Crown Vic's tailpipe....
I wonder if Total Seal will make rings for a Cummins pistion????