Oh hello there...
So I imagine I'm telling the same old story, "LOL I WANT TANK GUD", but I am having some problems I imagine have to do with a combination of my gear and my strategy.
I recently got my warrior to level 80, and I wanted to start tanking some raids. I was told by some guildies that with 26k hp and 540 defense I could start with 10 man Naxx as offtank. I can pretty much tank any heroic just fine, expecially single target (I often have a very significant threat lead). But then came Naxx 10... I was to be offtanking, and we started with construct. The first pull I attempted to pull one of the abominations off the MT (death knight), but just his AoE alone generated significantly more threat than I could to a single target. The rest of the instance pretty much followed suit.
After looking at recount, I discovered a large portion of my attacks were being either parried, dodged, or just plain misses. With only 25900 hp unbuffed, should I replace some of my +stam gems with +hit or +expertise gems? Do I simply have to suck it up and say I need better gear before attempting to do raids? Should I drop down from 545 to exactly 540 defense, and attempt to gain expertise there?
I would raise your expertise as close as you can get to 26 since that will eliminate Dodge and some parry. But at the same time try and not nerf your HP. Maybe try and switch your enchants around some to get it. I started with expertise to bracers and gloves, Icewalker for the boots and a titanium weapon chain that should give you a boost. Oh and try to befriend a engineer to get the combat shotgun made.