Ok, Maybe it's just me, but I fine that in Ulduar content most other tanks are far superiour to warrior tanks. I'm a warrior tank, have been since Vanilla, but as of late have been sort of turned away from the tanking aspect of the class. IDK maybe it's spec or gear, I don't have a problem with threat, but rather mitigation. Maybe someone who has met this problem and overcome it could help out?
The World of Warcraft Armory
Well warriors have a reputation of being very weak tanks relative to DKs & druids atm. Whether or not its true I dont know. However, I did speak with a very good guild the other day, and their warrior MTs everything including the 5/9 hardmodes they've done so far. I was shocked to hear this! So whether their inferior repuation is deserved or not, I really dont know. Good luck to ya.
A lot of your gear choices seem to be favouring Shield Block over the other avoidance stats. It is by far the least useful stat right now and I'd avoid it if you have other options.
You are also in the recommended minimum gear for Ulduar25, so you won't be able to walk into the zone and tank everything extremely easy at first, Ulduar bosses hit hard, really hard, so it's not going to be a walk in the park straight away and your healers will need to be ready for the huge hits.
I would personally steer clear of gemming pure avoidance (16 dodge gems etc) and stick with Stam.
My current guild uses a warrior tank for all of the hard modes (except Vezax). So it can be done.