Hi Igneuss, are you being out tanked in terms of survival or threat?
I have tanked 10/25 ToGC & ICC as MT and I think DK is perfectly fine except for Anub adds.
Other than having the right gear, enchant, gem, specs. DK is play style is slightly different from other tanks, it requires planning of cd and runes.
The best way to improve play style as a DK in my view is to practice arena. It is very hard to be a good DK as a clicker, so if you are a clicker you might want to change your playstyle.
Your gemming and enchant is ok, for rotation you can refer to Satorri http://www.tankspot.com/forums/f14/5...t-tanking.html
There are so many viable specs for DK so it is better to refer to the guide and find one that best suit you in terms of content and gear.