I went into ToC 10 last night, and my dps dropped like a rock. I can normally put out 4k dps in 10 mans with little problems
9Unholy DK). I read up and realized I was well below expertise cap...but Im not so sure thats the issue.
There can be numerous reasons, why your DPS dropped...like changes in gear, bad movement, unstable connection, forgot one disease, etc.
But generally said, you should fulfill the caps you need:
That would be 263 hit for melee hit cap, although for unholy, which relies much more on spells, you should give a look if you are capped with talents and support abilities (e.g. boonkin and shadow priest) at your spell hit as well.
Your Expertise should be capped as well (26), because it impacts your runic power generation, which affects your spell dmg, and because of the fact that, although you are unholy, your melee attacks still do the major part of your dmg.