So I went in thinking, "I never had a problem tanking SM Cath at 40 so this should be a walk in the park" Boy was I wrong. I'd make a pull and no sooner than I laid a TClap down did 2 or 3 of the mobs just turn tail and run streight to our mage.
So I run there and slap a few sunders on as fast as I could followed with a TClap as I didn't want to waste challenging shout that quickly in the fight. (even switched to Zerker stance to pop my Blood rage and Zerker rage for extra rage generation then went right back to defensive stance) and as soon as I laid down another stack of sunders on all mobs. 2x on each the same 2 or 3 damned mobs would head streight back at the mage.
It was so frustrating I was tempted to respec back to Prot so I could continue to tank like I did Pre 40.