Your gear seems fine to tank 10 man Ulduar. Being a JC, I assume you're also using the JC trinket instead of the dps one equipped on armory? That should bring your HP near 30k which is fine for 10 man.
Razorscale starts hitting the tank really hard once you start getting the debuff stack up, even with the best gear, so you need an offtank to taunt off you until your debuffs wear off.
If you were hitting enrage on XT that tends to point to a dps issue over tanking, since you were able to tank it for 8 minutes without an issue.
I have both the JC trinkets, but always considered the crit and 1k AP to be better than 1k HP... I have a stamina set that gives me 32k unbuffed and still crit immune... but the threat i do in it kinda sucks