I am in a mostly-casual raiding guild that has cleared BWD and is working on BoT.
Last night we were wiping on the Ascendant Council and I noticed my DPS was terrible, sub-4k. I cannot help but think that I would be better off tanking with my DK (10-12k DPS tanking). I think my gear is good for our level of raiding and I never have aggro issues, I just need to know how I can push respectable DPS while I tank.
Specc into deep wounds, cruelty, hold the line, incite and heavy repercussions. You basically skipped 50% of the worthwile single target threat talents
You can drop blood craze (only a pvp talent, heals for almost nothing in pve), drums of war (pvp talent, if you're on interrupt duty just make sure you've 10 rage for the pummel), gag order (pvp/5 man dungeons talent, but you're now a raider), impending victory (only useful 20% of the time on a bossfight, you should be safe without it).
Before pull put vigilance on the other tank, ask for md/tricks/thorns and use shield block + shieldslam as often as possible. At low vengeance and during shield block i'd just hit devastate if shield slam isn't ready, maximising your shield slams. Coupled with shockwave/heroic throw/concussion blow you got some neat aggro abilities there. Damage only rises if there's damage incoming but on council it's all about execution (don't stand in x, pummel y, get buff z). No damage equals to less vengeance and more importantly (for us) to less rage, thus you can't use heroic strike as often as you want to and that ability makes up for 30% of our total damage dealt in a high rage/incoming damage scenario.
DKs got buffed way through the roof (hello 20k deathstrikes with literally 50% critrate) and don't rely on rage as source of 1/3 of their damage, just imagine you wouldn't get any runic power while not tanking.
99 times in 100 if a Warrior (any spec) is struggling to figure out why their DPS is so low the culprit will end up being Heroic Strike and/or Cleave.
Remember these abilties do not trigger the GCD. You can use them whenever you want without interrupting your rotation. ANY time you have >50 Rage, fire a Heroic Strike (Cleave for 2+ targets). Your DPS will go up significantly.
You might also want to macro inner rage into shield block. It's not as optimal as having inner rage as a cooldown you manage, but in most situations it works fine, as shield specialism means you often get plenty of rage during shield block... just be careful not to overburn rage when you do have inner rage up.
Lose blitz, put talents in war acadamy. if you want multiple targets stunned, use shockwave. Blitz can also mess up CC's in 5 man's quite easily, an in my opinion just isn't worht the talent points. There are several abilities i would spec in befor i would spec blitz.