Your talent build looks excellent. I opted for Anhilation, but have been considering respeccing and taking that out. As well, I have Improved Icy Talons, for raids. My current spec is the same I used for Heroics when I first started, except some minor changes.
Have you considered using Blood Boil? It's an AoE attack, like Howling Blast, but only consumes a Blood rune, which goes perfectly with Howling Blast.
As well, stupid question: are you in Frost Presence? From what I can see, you are in gear similar to when I started tanking, and I had no trouble with agro, except from 3k DPS Warlocks, who liked targeting unmarked trash mobs.
Your talent tree should not be causing any Threat problems. My typical rotation goes: DnD, Icy Strike, Plague Strike, Pestielence, (wait), Howling Blast, Blood Boil, Blood Boil, Howling Blast, Icy Strike, Pestilence, Howling Blast...
As well, using Rune Strike whenever it procs and I have the Rune Power. Consider making a macro to use Runic Strike as often as you can
This macro should have you use Howling Blast, that you should be spamming, and, if Rune Strike is ready, it'll use it on your next strike. Consider replacing your whole rotation, with macros similar to this (Icy Strike, Pest, Blood Boil, etc.)
#showtooltip Howling Blast
/cast Howling Blast
/cast Rune Strike
As well, what glyphs are you using? Consider using a DnD glyph, for increase damage and threat. My major glyphs are Ice Bound Fortitude, DnD, and Blood Boil.