The one thing I can suggest is that I don't see Death and Decay anywhere in that rotation. I don't know if you simply forgot to mention it or figured it's such a staple in DK Tanking that it's not really worth mentioning, but...
Either way for me, I end up dropping DnD whenever I can. It can be very difficult to get and hold aggro otherwise, especially if you're blood. I switched back over to Frost probably a few months ago. the improved health really didn't compensate for my frustrations in not being able to hold multiple targets while focusing on one. So I use a combination of DnD and Howling Blast to make sure everyone's held in place as best as I can.
Another thing I also don't see is Blood Boil. After a (very) fail scholomance run back when I was in my late 60s, I learned the usefulness of using Blood Boil. It works alot better if all the mobs do have your diseases, but even without, it's still a quick burst of threat on all mobs within it's radius. great for quick stealing a mob back when someone's accidentally pulled it off and the threat-difference between the two of you isn't large. Of course that's presuming something hasn't changed and I missed it, which is possible of course, but it still works all right for me these days.
Your gear is waaaay beyond my level at the moment so I doubt that it's really anything to do with that although I'm not a hundred percent sure. Gems look cool too. Mostly I'd say you just don't have some things in rotation.
Also I'm not sure how well this works, but I did run across a useful little macro while I was poking around...if I understand it right, outside of combat it seems like the normal auto-attack. However when in combat, it automatically Rune Strikes whenever possible. Again, not a hundred percent sure how it works or if it works well, but the concept seems solid to me.
That's about all I got. If anyone has any contradictions feel free to disprove me. Otherwise, good luck!
/cast [target=target,harm,combat] !Rune Strike;Attack
"I don't have a dream, so I protect the dreams of others."~Inui Takumi