I think it was blowing head gaskets, injectors and turbo that gets coked up.
Here is a titbit for you. I had to go over 500 miles to get my 7.3 in 06. Why was I able to get an 03 or 04 within 50 miles of where I was? I finally got an 01 Excursion with the 7.3. The dealers were trying to palm me off with a 6.0. I asked why 7.3s were so hard to come by. They told me that the owners were driving them into the ground. Yet, they were insisting that the 6.0s were so good. Yeah, right. That is why the current owners were dying to get rid of them. Sure.
http://www.powerstroke.org/forum/6-0l-problems-forum/