There is one thing left out in your original posting, you never said what kind of diesel you have!
If you have a 98 or 99 606 engine, the levels of soot will be much higher due to the new epa standards that they had to pass.
Not to get to techy into this subject(again), but if you do, or do not have one of the new diesels, use the new oils made for the 98 engines.
These oils have one massive improvement over the old ratings, and that is there ability to hold soot longer in suspension.
Please folks, dont get into this oil versus that one, just remeber the new ratings of CG and CH 4.
98 300 DT