I just filled up with my 2nd tank of 15ppm at a local Kroger store. My truck has never smoked before other than a slight haze WFO on Banks Speed-loader setting. Now I'm puffing black smoke in Level 4,5,6 & SL. Not a huge amount, but enough to where I notice it. Also seems like my mileage dropped about 2mpg on the last tank, nothing different driving wise. Is the ULSD fill-up just a coincidence? I had been running the mid-level ULSD that they were using for a while. I believe 500ppm?, with no problems at all. I run PSD in the truck every other fill-up unless I'm dead empty. I haven't changed out the fuel filter yet, but plan to shortly. Seems fine as far as power goes.