Okay, one thing I can tell you right off the bat.
You need to seriously think about your glyph choices.
Unless these are wrong, you have:
Glyph of Frost Strike
Glyph of Icy Touch
Glyph of DnD
Your rotation as a single-target tank should be PS>IT>Oblit>BS>BS>FS>Oblit>Oblit>Oblit>FS, repeat.
I think you can tell what your most used ability is. And I think you can see why having 20% more damage on that ability is mighty fine.
On multiple targets, your rotation changes with the glyphs. In general, you will want to BB and HB as much as possible during this. If you take the glyph of HB, you can turn all your Pests in a rotation into threat instead. Furthermore, freeing up that IT every other cycle allows for another Oblit--you just tab through the mobs and use it on the one with the least threat towards you (or the one threatening to run towards a party member).
The Glyph of DnD is just WAY overkill for frost, in my opinion. If you need to use it, HB and BB should be more than enough to prevent the mobs from going elsewhere.
So, right off the bat, every frost spec I make (unless it is SPECIFICALLY for AoE OR Single Target tanking), has the Glyph of Obliterate and Glyph of Howling Blast.
The third is up to you. Frost Strike means you can get more of them in. Unbreakable Armor is mitigation. Disease means you don't have to ever use IT or PS after the first use on any mob, AoE or boss (but I hear it is glitched right now).
But, rest assured, your gear is good. The only thing I'd work on ASAP is getting some tanking or better DpS trinkets, but I know how annoying this is right at 80 (seriously Blizz, would it have killed you to give us some good quest-reward ones?)
You also need to work on your gems. Try and get 540 defense through the non-metas, if possible. That gem is just so inferior for DKs. I recommend you try and nab one of
these or
these.
And the minute you can get your gear to 540 defense without SSG, do so. You then have the choice of keeping it (for 3% avoidance and 2% health), or going for Sword Shattering (4% avoidance).
Oh yeah, and do all of the Sons of Hodir quests everyday! You want to hit exalted so you can get
this. Oh, and you want
this from the Argent Crusade.
The only other advice I can give you without seeing your armory is to try leveling up JC or BS with the gold you get from your dailies. That'll let you get higher stats through prismatic gems or two additional sockets.
Try making your build on WoWHead and link it it here.