Since your main issue is threat i would suggest respecing for +5% dodge to make use of your RS more frequently since it is a high threat and high damage ability that should be part of your rotation anyway. Since your hit is - as mentioned before - way too high, you could take the point out of thosde 3% hit for spell and put them into the dodge and a 100% crit HB. Use it right after getting you diseases going, instantly after pulling, raidbuffed it should crit for at least 9k, thus granting you about 16k threat. This gives you a headstart over the DPS and will increase you chance to get a RS proc right away.
Also, make sure to pull with DG, granting that the boss will attack you, and only you, for a short amount of time unless he is taunted of. Eventually, your abilitys comeing of cooldown will overlapse, but as long as you keep in mind that RS is your first priority threat strike will make this easyer to deal with.
(This is meant for boss threat only, let me know if you need help with trash threat as well)
Finally, I am sorry for my crappy english and you may find some typos in this post, but since i am austrian and not a native speaker i guess you will forgive me .
"Warriors aren't viable as tanks!" - my guildlead