VERY quickly done because you still have given us very, very little info. There is a good amount of room to play in that build. For example, you may want Morbidity, which I would drop some KM or Bladed Armor for. Do you run with a Shaman? Then you can get rid of Icy Talons and Imp Icy Talons for the additional threat of KM/Bladed Armor/Morbidity. You could take Death Chill for additional threat spikes every two minutes (but I personally don't think it is that useful with 5/5 KM).
How are your healers? Are you doing magic intensive fights right now? Maybe take Acclimation. Do you have a proper resistance aura during those fights? Frost Aura may work nicely.
And you still haven't told us WHEN you lose threat. Are you good with single targets? Do multiple mobs give you trouble? How are you on Omen?
And tanking won't have any kind of real rotation, just a starting point. Since we use DnD, that takes away 3 runes and really eliminated the possibility for things to proceed smoothly. You will always have to judge. Some times, you won't be able to use HB at all a rotation because you need to refresh your diseases and Pest. Sometimes you can use two-three HBs in a rotation, because your diseases are fine until the next, where you will will reapply them, pest and DnD.
Sometimes, you won't need to use DnD (it IS nice threat, but much less appealing on single mobs if you can go without), and you can follow more of a DpS-based rotation, using Runestrike as much as possible.
If you give us more info, we can help more. So, first, try answering these questions for us:
-Do you run with a standard group? Do you run with any specific people, but the overall group make-up varies? What specs are those you usually see?
-What are you running? Your gear seems decent, so I'm sure you are in Heroics. But, which one? Are you talking about Naxx?
-When are you losing control? Multiple mobs, single mobs? Large groups, small groups? Bosses? Adds?
-Do you have Omen or a similar threat meter?
-Do you have an addon to help watch rune CDs?
-Do you use trinkets with "use" effects?
-How cluttered is your interface?
These may help us identify some of our problems.
And, if you would, we could really use your armory. If you don't want to give us that, at least link your gear and professions.