Dodge and Parry both suffer from something called Diminishing Returns. Essentially the more of one you stack the less benefit you get from stacking it further. So in order to maximise your avoidance (parry +dodge chance) you want qual amount s of ratings for both stats. However due to the talent you linked Parry is slightly more valuable to warriors than dodge, How much more valuable is based on 2 things, how much master you have (more mastery means parry is worth more) and how much total avoidance you have (more total avoidance rating means parry is worth less). THIS graph shows the relationship nicely. We get rage from attacks we dodge and parry.
Mastery VS stam: first off you need a certain amount of stam for the content your doing, most of the time this will be enough from the gear of previous tier of content (so full 359s has enough stam to start out in firelands). Now Imagine the profile of damge taken if you never blocked:
From a healers point of view this is quite spiky, some swings you take no damage, other you take a full hit which in Firelands could be about a third of your health. so they have to heal very reactively, having to hit the fast expensive heal alot. this will generally make them oom faster.
Now Imagine that 50% of those hits where Blocks
you're no where as spiky and you're healths no going up and down as much, your taking less damage and its coming in more regular manageable chunks, so the healers don't have to be so reactive and can just use the run of the mill cheap heals to keep you up.
it easy to keep up with a steady stream of damage, an unpredictable big or nothing damage makes healers have to work. It's alot easier to press one button at the right time, than having to choose which of the three buttons should press at this time. Your health pool was spiky before you just didn't notice it because you were (wrongly) confident that your gearing strategy was optimal. Now you don't believe its right so you're looking at it and clutching for justification one way or the other.
I really don't see how taking less damage overall and being easier to heal makes your job or the healers Job harder?
To be Frank you're using 2 stam trinkets, so yeah you will take a "shitload" of damage. Get 1 or 2 mastery trinkets. you've got around 7K more unbuffed health than me, but around 10% less block. I've never had a negative comment regarding my healability unless i stand in something instagibby, I occasionally get the "I'm bored take some damage" comment.
When you have aggro are you making sure you're using shield block on CD? are you making sure that the Thunderclap and demo shout type debuffs are up 100% of the time (either from you or anyone else). are you using your CD's effectively to pre-empt predictive damage spikes? including on-use trinkets?
You have a very odd spec. the standard raiding spec looks a little bit like this. the points in Imp revenge can be pulled into thunderstruck for a higher DPS, but slightly more difficult rage management spec, or Safeguard for or Gag Order (though Gag Order is a pretty damn pants talent). I wouldn't be surprised if your having threat issues as well with that spec.
What's your rotation?
I see on your Armory you have stam trinket on still (from the 2 Tengenstein said) If you do not have another the TB one is nice and gives a nice resist CD or the dps with the str CD and it can be used to help build agro (not that its needed much anymore). I also like the 60 str + 35 mastery head enchant, since str gives parry chance as well and basic gear has plenty of stam for you to live. On your Boots being a Warrior I think the 50 Mastery would be better than the 35+runspeed as you have alot of mobilty without it.
those would be my only changed to the way you are enchanted and the one trinket, as for what to reforge good rule of thumb that has worked for me and War tanks that have OTed for me is parry 1-2% above dodge seems to be about right not to suffer Diminishing Returns so bad but everything you can into Mastery (until you hit CTC sure if you do not know it you can search it easy)
(My main is a pally tank but I play around with a War tank alt. But really they are close in how you should enchant and reforge)
I would never give up runspeed (well maybe on Baleroc). RUn speed is awesome, the faster you move the less time you need to spend moving, the less time you spend standing in the crap, and the easier it is to kite stuff.
With Heroic Leap, intevene, and charge I would rather have the block if I am not CTC, but I will say its probably more personal pref, as in the begining I was looking for every ounce of survivability.
the 15 mastery difference in the boot enchants works out to be about ~0.09% block chance if my math hasn't failed me. Personally that's a tiny amount of survival to give up for the movement speed. Honestly though try it for a ouple of weeks then go back, if you don't notice the lack of mobility that's cool, but i can't live without it now, it just allows so much more flexibility whilst tanking.