First glance: you're really low on % block. You should really aim for about 50% with the crafted & welfare gear flying around.
Your specc looks ok for running heroic dungeons, if you have aggro problems you might want to put some points into War Academy and Deep Wounds (dropping Gag Order and Blood Craze first)
Minor - Furious sundering don't work on Devastate. Enduring Victory is meh, 5 seconds more.. 20 seconds is already a huge leeway for us it in the same battle after getting a killing blow and regulary 25s are to little to use it on the next camp with setting marks, CC and so on. I'd use demo shout and berserker rage instead.
Gems: you want mastery
red = parry/mastery
blue = mastery/stamina
yellow = mastery
prismatic = mastery
Reforging: you want mastery on every item, aim for avoidance stats afterwards
head - dodge to mastery
wrist - expertise to mastery
weapon - haste to mastery
shield - hit to parry
ranged - hit to mastery
gloves - parry to mastery
legs - parry to mastery
feet - parry to mastery
ring2 - expertise to mastery
trinket - parry to mastery
With those tweaks you'll end up at about 50% block with slighlty lower avoidance numbers but that's okay - as a block-tank you regulary want smoother damage income over higher overall damage reduction.
Get the Mirror from Tol Barad (trinket), will work well with magic damage.
As a Warrior, you should aim for Parry to be just above Dodge in ratings, but not far above. You receive a lot more damage reduction from balancing rating than you do from trying to increase HtL uptime a tiny bit.
(Note that Strength (and thus Parry) buffs roughly counter the Windwalk buff, as both are worth ~200 rating)
Agree with most of the above, with small exception:
If your healers are kind a slow, you may opt to go for more Stamina once Dodge%+Parry%+Block% >= 72.4%
That should allow you to use SB to complete the combat table when it's up (often referred to as SB Unhittable, as you won't get any normal hits on you with SB up).
The first choices would then be Mastery/Stamina in yellow, Parry/Stamina in red & full Stamina in blue gems.
You'll also want to get the Eternal metagem, which provides far more overall damage reduction and with SB unhittable also greatly improves the guaranteed damage reduction.
Thanks for all the advice guys, I am mostly tanking heroics as my schedule doesn't let me raid much. I did get some new gear, shoulders and helm from ZA/ZG. Love tankspot vids, they are a lifesaver, literally
Again thanks to everyone on these forums that help out!