You have far too much defense (560 instead of 540), and it's partly due to the fact that you gemmed your crab with defense instead of stam and stam defense. Your gloves also could probably do without the 34 defense. Also, avoid missing stamina socket bonuses, like your boots.
Definately chase after new shoulders and bracers in HToC (Bracers from Black Knight, shoulders from priestess cache).
If you accumulate enough badges, the platinum mesh cloak from valor badges is better than your current cloak, as is the tanking ring with the same badges. However, running a raid is probably more beneficial.
You should easily be able to do nax 10/OS10/voa10. I wouldn't put Nax25/OS25/EoE10 above you either, although VoA25 Emalon may be abit of a challenge for you.
I would mention that I find ToC gear to be DK friendly due to shield-stat less tank plate, the heroic gear is a good for situational tank sets.