I have been a long time user of Dieselkleen and honestly I am not sure why doesn't seem to really do anything? I have also used 2-stroke oil as well which made my truck much quieter but, for me at least, cost some HP.
I have a 2003 F250 6.0 Powerstroke. I recently tried a product which is getting rave reviews (for 6.0's anyway) called Archoil 6200. It seems like a scam to consider that you add 3 teaspoons (half ounce) of the product to 29 gallons of fuel but that's what it calls for.
For my first dose, I added an ounce to my tank and topped off. Honestly I didn't expect to see ANY change in operation but I was very wrong. I have had this in for only 60 miles, and my 6.0 is FAR quieter, quieter than using 2-stroke. It is also smoother too. Not sure that I am seeing any benefit on power, and mileage is about the same (21-22 hwy) according to the overhead display, which actually is pretty close to hand calculated.
They also have an oil additive which I am planning on using on the next oil change. I have had great results with Rev-X, and have heard of better results with Archoil 9100.
Within just 60 miles, I notice a big difference, not in performance but drivability I am already sold on the 6200 product. I did a search, read a lot on it and there is nothing negative, a little neutral and a lot positive. The fuel additive is supposed to work well with Cummins, Duramax and us Ford guys. Cost per tank is on-par or less than the other additives.