Dealer Tech here....Funny part is, the newest design has been trouble free mostly, other than a few software updates. And they are all getting a new CP3 injector pump, under a recall. The big thing on the early ones, was too thin of an oil/too long change interval, and EGR cooler failure. EGR cooler was recalled, and they updated to 5/40. I rec 7.5k LOFs max but some people push that to their detriment.
2 reasons these are dead(and other 1/2 ton diesels), well 3 sort of. 1, people got burnt on engines(eco diesel), so no way are they coming back for a second go around, 2 typical buyer was a gas person, and had no idea how much maint. was on a diesel compared to gas, and 3 diesel fuel alot higher right now.