I also have a '02 Ford Powerstroke & I have found that the use of 2-cycly oil mixed 1 oz. to the gallon works wonders for my engine. It quieted it down considerably, runs better & I even picked up a mile or two a gallon mpg-wise.

Keep in mind that the additives such as PS Diesel Kleen, etc., are full of things like acetone & other solvents. Might be OK for an occasional treatment, but nothing you'll want to run in your engine forever.

See: http://www.thedieselgarage.com/forums/showthread.php?t=57914&highlight=2+stroke+oil