I ran into a guy that has a 7.3L NA in his F350. Seems to be fairly knowledgable with diesels. Runs the Stanadyne additive, has a Racor filter, coolant additive, etc, etc... He says he puts a quart of ATF in with a full tank of fuel every so often to clean out the engine /forums/images/graemlins/confused.gif I've heard of doing this on a gasser to make it run real hot and burn out any carbon build-up - but on a diesel?!