I ran the daily with this tank today, and for the life of me, I could not keep him alive. My gear isn't spectacular but it's decent, and I've run many a heroic where I just keep up a LB stack and a Rejuv and never worry. I've even held my own in some pretty impressive raid groups.
So why couldn't I keep this tank alive? He was doing his job, everyone else had tiny fractions of his threat, and the dps was pretty good, everything went down quick enough. I don't think I screwed up in any obvious way. In fact, I was paying more attention to this run than I normally do since it was going so badly.
All I can think is that since the pulls were mostly singles, he was taking more spike damage than we're built to handle. Also, several deaths were caused by my getting one- or two-shotted by random charges or aoe. Wearing cloth and skimping on stamina has it's drawbacks.
I'm just trying to figure out what went wrong so I can do better next time.