Why did you socket for Crit?!?
If you are going to socket for a Yellow Socket, Hit Rating or Defense should be the only two stats you socket for.
The "acceptable" chest enchant for a Tank is 275 Health or the Defense Enchant not stats especially +8 stats.
Need to get Expertise up to 26. It could be the expertise or the combination of low hit rating and expertise that allow people to pull off of you.
What are your rotations? Single Target and AoE?
What are you doing on a single target?
With very few exceptions I have never had a dps pull off of me with a single target, even in a 25 man raid with some dps doing over 6k damage.