My tailpipe is always covered in black carbon deposits as well. I don't have the symptoms you have, but last weekend I got a CEL (1404) and I changed out my EGR. My VX is running better for sure. A lot more pickup and so far no stumbling or chugging like I was before. IMO, I almost think its a good idea to replace the following around 75k, symptoms or no symptoms:

1) Fuel Filter
2) Fuel Pressure Regulator
3) EGR Valve

I have done all of those swaps and so far so good. I hope to get to 100 with out any more issues, but we'll see.

Bart