Kologarn favors avoidance tanks slightly because stacks have a better chance to fall off or be avoided all together so they spend less time with the armor debuff.
You're gear is fine. If you're dieing go for more avoidance gear and less threat. If you're just worried that you're taking more damage, change some glyphs out for last stand ( wont lower damage I know) and shield wall.
Are you making sure demoralizing shout is up ? I got into the bad habit of not using it in naxx ...because training you to be a bad player is what nax was good for. Imp demo shout is also a good way to lower inc damage. It's a hit to threat but worth it if living is a problem for you.