Spec: You need 5/5 Blade Barrier (1% mitigation for 1 talent point, why wouldn't you take this?) and 5/5 Bladed Armor (huge chunk of AP for threat) and, since you're using a 2h, 2/2 2H spec (again, huge chunk of threat). Necrosis and Ravenous Dead do you very little good as a tank. Icy Talons doesn't really benefit you either, although if you don't have a Frost DPS DK or an Enh Sham in the raid I can see why you take it.
Are you using single-disease for raid bosses? It can work, but if you run into threat problems you're better off with two diseases to buff your Obliterate and Blood Strike.
Gear: Wrong rune. Even if you're over 540 from gear alone, you should still use SSG for the extra HP (the defense adds a decent amount of avoidance as well).
Gems are all over the place. Get the armor meta (32 stam 2% armor), get rid of those hit gems (you're already way over the hit cap, why gem hit?), never ever gem parry. Your expertise is very low, replace those str/stam gems for exp/stam. I would recommend replacing Corpse Tongue Coin for tanking hard-hitting raid bosses, a stamina or armor trinket would serve you better than a dodge one.