2004 duramax black smoke and sputtering when

Black smoke means "fuel not being combusted" or "runnig rich". I have no doubt you have gasoline. Your spark may not be burning the gas. Is there a check eng lite? If EGR was sticking, you would probably get a check engine light for this. If your truck has a Vortec design, I would find out if you need a new "spider". What is your mileage? Are you due for a tune up? What spark plugs are you using? Vortec? "Not all the time" sounds like intermittent. When was the last time you changed the fuel filter? Can't hurt to change this. This would be the actaul starting point for me. I would change the fuel filter which is under the driver under the chasis. You will need a 16MM and a 20MM. USE ONLY LINE WRENCHES. You may need a fuel line disconnect kit too depending on your model. Notice it only happens on acceleration? that is when you are forcing even more fuel thru the system, but not enough of a fuel stream make cause sputtering and when the fuel comes thru too rich that would be the black smoke. It sounds like you have the 2 extremes. is there afuel regulator on your vehicle? If so, you may need to change that too. Good luck.