FWIW, SIL is in the trucking business, lots of people are having not so good luck with the newer engines.  Both on the mileage and the longivity.  I know of two people in the past year that have spent big bucks, (10-20K more) to either change out ACERT engines or build a 'new' truck from a glider kit so they could run older C-15's.  They claimed they could pay for the change with the fuel savings alone.

I do know for a fact the one Cummins tier 3 engine they own has had multiple problems with the EGR 'system', each time the bill was in the thousands and wasn't covered under emmissions warranty.  The truck has less than 500K on it, bought new and always maintained to a 'tee'.