If the plugs are black with fuel, you're obviously running way too rich. This is either due to too much fuel or too little air. Make sure the air filter is not clogged and that there is no debris on the mass air flow screen. If the vehicle is actually misfiring and you have new plugs and wires installed, then you'd be looking at injectors or possibly coils breaking down. If it's missing on all cylinders, it probably isn't all six injectors, or all three coils going bad, it has to be something in common. That could be something like a clogged catalytic converter causing excessive backpressure and misfires. This will usually foul out the plugs if bad enough. You didn't mention a problem getting up to speed, which is usually a symptom of a badly clogged catalytic converter. The other possibility is a leaking fuel pressure regulator. This is far more common and if the diaphragm is ruptured, you'd be dumping raw fuel right down the intake which can also cause the problems you're having. To check that, you can remove the vacuum line from the regulator and see if any fuel leaks out. This is best done when the engine is hot (careful of fuel spillage and fires). Also, faulty oxygen sensors
can cause the computer to dump fuel if they are not reading correctly. I would recommend getting it scanned again, and probably taking a look at the live data on the scanner to see if all of the sensors
are within range.