Upgrade your weapon. il43 weapon isnt going to help you in any dungeon as a lv51.

DRK tanks aren't the greatest around that level. I find that since they start at lv30 that there is a huge learning curve compared to PLD or WAR who leveled from the beginning before they can get into the flow of things. This generally is only true of people getting into tanking for the first time and dont have any other 50+ tanks.

Having double BRD wasn't going to help you at all either.