One huge problem with the 6.0L PSD was people using them like a gas engine. Hop in, start it up, drive a few miles to the grocery store, then back home. Repeat over and over. Pretty soon the turbo vanes and EGR cooler is getting clogged with soot because the engine isn't getting to operating temp and staying there.

The happiest owners are those that let the engine work. They tow with it or haul with it, which allows the the junk to be burned off on a regular basis.