I need help with my frost talents, I can't seem to hold threat when tanking. My gear is pretty solid, I'm slightly over Def cap, and have 26000 HP. I tend to do AoE tanking using DnD, IT, PS, Pest, ERW, BB, HB, BB, HB I toss in Frost Strike every time its up. Aafter the initial rotation, I use BB, HB alternatly, and Frost Strike/Runestrike when its up, refereshing deseases as necessary.
I have looked over your spec. I don't advocate the idea that there is one right spec to tank in, in fact the spec needs can and do change with gear level. For example I recently respecced to increase runic power generation, because as my avoidance went up I found I was using RS so much that I was too rp starved for a good rp dump at the end or my rotation. That being said, I am sure looking at your spec that your threat problems are genuine.
First off, when you hit 80 there is a bit of a gear gap, you need to tank heroics but the gear that you need to def cap for them leaves your threat output wanting. To some extent well geared dps'ers are just going to have to be patient and hold back to keep from grabbing aggro until you can get better gear.
Second... your spec
A) loose Improved Icy Tallons... its a great raid buff but it isn't doing crap for your tanking, and the points you spend to get down to it are hurting your build... stop at Improved Icy Touch.
B) Pick up Anhilation
C) Drop Merciless Combat... your threat problems are likely to be during the beginning of the fight... when the enemy is low on health you should have a deathlock on aggro already.
D) Pick up 2 hand weapon specialization
Third.... Macro Rune Strike to every move... its your single target bread and butter and should allways fly out when it procs
Fourth... find some really patient friends who will run heroics with you until you until you have some better gear and figure out what you are doing... really really really patient ones.
Oh.. and Don't glyph IBF, if you are defense capped then that glyph isn't doing crap for you, glyph Death and Decay instead.
There are about a thousand things you need to learn to tank well with a DK, and most of them can be found in these forums. Start to learn the language, read, and apply.
Personally, I'd drop Acclimation (3 points for a chance to help you in some fights, seems expensive) and Litchborne (not worth the point since the dodge buff was taken away) and put them in 2 Handed Weapons specialization and Morbidity. Also, I agree that you should Glyph DnD. If you're having threat issues, DnD is your best friend followed by RS, HB and BB.
Get in the habit of Death Gripping your pulls into DnD, then dropping HB (hitting Death Chill first if you can), you'll pretty much have the mobs attention.
Talents - Agreed, drop Icy Talons/Imp Icy Talons. Shift those points into Two-Hand Specialization (Blood), Annihilation (Frost) and Hungering Cold (Frost).
I would also shift the three points out of Acclimation to Chillbains. The snare effect prevents mobs from quickly getting out of melee range, so you have more time to change targets and apply attacks, taunts, etc. before losing control. Be aware that you will see "Immune" often on bosses, however, which takes getting used to seeing.
RE: Hungering Cold - this ability is far more useful than folks realize, even in raid situations, as it provides a non-rune method to apply Frost Fever. Again, Chillbains is a factor, as either lock down mobs or snare.
Glyphs - Drop IBF & UA Glyphs. Load Frost Strike & Obliterate instead to maximize single target threat. This shifts your style from survival to dps/threat.
Frost vs Rune strikes - while Frost Strike is common, you need to maintain/reserve 20 RP at all times for Rune Strike. Macro'ing RS into all your abilities is awesome, but you still need to have the RP available to use it. Per point of damage, RS does 1.5x the threat compared to Frost Strike, plus RS cannot be dodged, parried or miss (FS lost that perk in the 3.2 patch).
Rotation - I normally open on AoE with DnD (far edge touching nearest mob or the farthest caster, to ensure I'm building threat on those targets), then HB on mobs as they're in the DnD, then Blood Boil. The HB glyph applies Frost Fever, improving BB's damage. After that, I shift to HB, Obliterate, 2x BB on AoE packs. I find the one disease setup adequate for threat/dps, but also very smooth.
If you want Plague Strike, change the second rotation to:
Obliterate, HB (cooldown comes up), wait for death rune... PS using Death rune, THEN pestilence.
This is going to sounds weird, but since you say you have 26k and your armory shows that, make sure you are in frost presence. You should have closer to 30K.
Secondly, change your Sigil to one that can aid your tanking, a dodge one, or even a dps one. The extra defense from unfaltering Knight won't be as beneficial.
Thirdly, gem for stamina or stamina/avoidance. Another option, though I do not know *REPEAT CANNOT CONFIRM IT WILL BE BETTER* is to gem exp/stam. You are right at the dodge cap, but with two weapons it might be beneficial to hit parry cap as well.
Fourth, do not use FS until you hit RP dump, RS does more for aggro and isn't on the GCD. Macro it into your four main strikes.