2012 D6K Fuel System Problem

We are having problems with our D6K fuel system. Throwing code but no problems show up on computer. Losing power. Appears to be problem with the high efficiency fuel filters. When those are replaced all is well for a while then problem reappears. As near as we can tell it is a problem with the fuel. There is a black film inside the tank. One mechanic says it is a fungus in the tank. Has anyone experienced this problem? Mechanic says take tank off and steam it out. Will this work or...

2012 D6K Fuel System Problem

2012 D6K Fuel System Problem