Spec and glyphs need a little TLC. Try speccing 53/18 instead. Crusade will give you a lot of threat, especially in ICC since almost all the bosses and mobs (to my knowledge) meet the criteria for the full 6%. (the three points in Divine Sac/Guardian can go pretty much anywhere, the point is that you only need to spend 3 points to get to the next tier - all the options for those 3 points are kinda mediocre) (likewise, there are a lot of options for the third glyph)
Also note the Seal of Vengeance glyph. Even if you're over the expertise soft cap, a static 10 expertise is a huge amount of threat. Since you're under 26 expertise (the soft cap), it's pretty much required.
Gear looks very good. If you have a Brewfest trinket, I'd use it in place of the Essence of Gossamer since its proc is worthless. I'd also switch out the defense enchant on your shield for 18 stamina, since you are already over the defense minimum, and stamina > avoidance in current content.
Also consider swapping out your Armsman enchant for +18 stamina or +240 armor. Since you're gaining a lot of threat by respeccing, you can afford to lose the 2% from the enchant in exchange for more survivability. This is definitely optional though.
Keep the defense. Defense to shield is a superior enchant to +18 stam imho.
I would have to disagree. I'd rather 180 health compared to defense any day in TOC or ICC once I'm past the defense cap. Stacking health is just what tanks do now a days to stay alive, and 18+ stam is nothing to shake a stick at (unless you just like shaking sticks).