Stay away from a Cat?  hahahahahah.  That is is why NAT is the last place I would ask a general question like what semi to buy???  Get so many different answers on the opposite sides.  For the record we have a 3406B in an 89' KW T600.  Has over a million miles on it and it's never been overhauled.  Can't say that about any cummins engines we've ever owned.  Plus it starts better too.  Big Cams are a step down and yes we own one of those too.