I have an 2003 dodge 5.9, about two years ago I replaced my oem filter and air box with a K&N filter and cold air box. Recently while servicing the filter I noticed a layer of fine dust inside the tube, this dust has somehow made it throught the filter. Is this normal for this filter, am I doing something wrong or what? I have since went back to the oem filter, but lost some mpg's. Does anyone have an idea?