As Stealthy pointed out, your spec seems a bit strange. Depending on your DK's main activity, your spec and rotation can be more important than your gear in my opinion. Glyphing is also extremely important. You need to make sure to keep your glyphs in line with your spec and rotation as well. There are some excellent specs and rotation help In This Thread. I believe you may find what you are looking for regarding common DPS questions. (edit: grammar ugh!)