black fuel

Last time fuel filter was changed? Do you have a davco fuel filter or stock setup? Sounds like bio fuel crap growing in your tanks but could be something else. Has truck sat around at all and where did you last fuel up at?

 

Probably need both fuel tanks washed out.

 

Injector seals leaking letting soot into the fuel

 

fuel algae from the sounds of it.

Clean it or biocide treat the tanks.

Either way, you are going to have fun cleaning this up.

 

Is it possible you're tanks are dirty or someone put something in the tank first thing I would do is take the fuel lines of the top of the trans and run it from a separate container of clean fuel you can add about 1 qt of 15w40 oil in about 5 gallon bucket and run both supply and return in separate containers that way you can see if it cleans up the fuel or when it does if it doesn't then It had to be an engine issue but try running it from a clean container of fuel with a small mix of oil

 

First get rid of the stock filters when you can and change over to a DAVCO filter setup, much better system and you can see the fuel in the filter setup. If its Algae from biofuel then, you will have to treat several times and filter change several times before it goes away. Its typically black looking like you are describing but so is leaking injectors which goes into a bigger issue of needing a six pack of injectors real soon. You can replace one but what happens typically is that the others are soon to go also and then you end up paying more money in the long run. Have you had an overhead done? ever?