Benediction is entirely worthless with your current build. If you're having mana issues, tank more, keep Divine PLea up more. If you're still having mana issues (usually because you massively outgear the content, which from the looks of things you won't except maybe in heroics), take a 2nd point in spiritual attunement. That's a hell of a lot more mana return for several fewer talent points.
Reckoning isn't entirely worthless anymore, but is still the worst threat talent available. While you do need 3 points to go further up the three, Divine Sacrifice is an amazingly useful spell for raiding if you're ever NOT the aggro target (Fights with no tanks, with down phases, when you're offtanking, etc). Whether you take Divine Guardian at that point for the longer sacred shields (if you don't have a paladin healer, keeping it up on yourself is a big buff) or imp Hammer of Justice is a flavor choice, but I always go for the hammer so I can dependably handle my own interrupts/stuns on fights where I can use them. It's a lot of flexibility.
Get up the ret tree by taking Heart of the Crusader, and either a point in imp BoM or 2/2 judgements. the 2nd point in judgement doens't help your maintanking rotation, but is great for adds, trash, etc. Heart of the crusader is a huge raid buff and you won't always have it brought in a 10 man if you don't bring it yourself.
If you're going to spring for epic gems, why are you being cheap about your boot/shoulder enchants? Grab 22 stam or Tuskarr's to boots, and since you don't have the hodir rep drop 10k honor on the PVP shoulder inscription for 30 stam, the best effective health enchant available there.
Speaking of your boots, outside of a threat specific set tanking gear should never have a straight strength gem in it.
And on the topics of gems, your'e way over the 540 defense minimum. While defense still provides valuable avoidance, at your gear level stacking Effective Health is what's going to allow you to progress onto higher end content. Lose the pure defense gems in your sword and shoulder, switch them to def/stam if you want to keep the socket bonuses. Both bonuses are relatively poor though, so I personally wouldn't bother, but you prbably might as well since hopefully you'll be exchanging Seal of the Pantheon for The Black Heart as soon as possible. Then you'll need the defense (although the 15 resil from your Gladiator enchant WILL stack with defense for maintaining uncrittable status).