Alright i see a few things you can change.
1) Your glyphs- DG and DND are not the best for tanking. As an 80 tank you dont need the refreshment of DG as a tank (I only use dg on trash pulls to get adds that go on overzealous adds,) Also for the dnd glyph you dont dnd that much because you have HB to get your aoe threat. I would replace those 2 with icytouch and rune strike glyphs.
2) Your spec. It seems ok but if you have trouble with threat i would switch to something like this Talent Calculator - World of Warcraft. But a lot of it depends on your play style. Im a personal fan of the HB glyph and the single disease rotation so i wouldn't spec into Epidemic, but if you don't like that then the disease glyph works just as well with a 2 disease rotation. It all depends on the play style.
3) For your gear i am a personal stam stacker. Once again a play style thing. I love having a large health pull and personally for the content out now thats what my healers prefer. So i stack stam in every slot except for what it takes to meet the meta. So i would stack stam in every slot except the belt and just keep it 10dodge/15stam. Also i would look into getting the armor enchant for your cloak because your over the uncrittable point so armor enchant might help some more.
Your major weakness is expertise. This means Obliterates/Frost Strikes are liable to be dodged as well as parried, making it important to correct. The +15 Expertise enchants to gloves/bracers and trading 'red' sockets to use expertise or expertise/stamina gems are options. You are trading your avoidance for threat, but in this case, it will benefit you overall.
You can drop Virulence, as evidence that the 'spell cap' on many DK abilities isn't the full 17% for normal casters. With typical hit capping (263 for you, 8% melee, ~10.6% spell), you'll be hitting with a very high percentage of 'spell' abilities like Howling Blast.
I do agree that the Death Grip/DnD glyphs are wasted. The 'usual' set for Frost is Obliterate, Frost Strike, Howling Blast. For you, I'd go OB/FS with Glyph of Disease to maintain the two disease set up you're using currently. Note with the dropping of Glyph of Desecration, you probably want to move those 3 points elsewhere, such as Epidemic, Merciless Combat and/or Chill of the Grave.
According to wow-heroes, Uld 10, EoE 25 should be easy, and ToC 10 and Uld 25 should be moderately difficult at your gear level.
Edit: It would also behoove you to get a second profession. Cheapest, easiest and most useful for a tank would be mining, for the +60 stam profession bonus. Get Dual Spec, create an off-spec with On a Pale Horse, then take a Saturday and run around leveling Mining. Prospect or Auction everything to recoup the 1k for dual-spec, or save it all on bank alts to use for powerleveling Blacksmithing some day.
You have gotten all the gear out of heroics you can and i doubt 25man naxx will hold many upgrades. I would run a non hardmode 10uld/toc. You should have an easy time with those. a big upgrade would be the pants off of 25man maly which you should be able to tank if not then ask to ot the adds during the second phase. But if i were you i would go to mmo-champ and look at the loot tables from uld and toc and look at the gear and make a list and start going for those upgrades.