I think everything has been said by others but I still want to say it too.

You have two different problems really. The first is that many of the people who queue for old dungeons like these are spamming them for an extremely grindy quest and they want nothing more than get in and out as fast as possible and don't have much patience for complications. And we're before an expansion, people are bored and edgy, most of the veterans don't play much at all, yadda yadda.

The second problem is that the rules change completely at 50. DPS classes finally get some worthwhile AoEs, and will deal more damage if they're free to choose their targets. Trash mobs are a lot less threatening and healers have more tools to keep you up anyway. And the goal itself changes from "get this thing done" to "get the best possible time".

What this means in terms of tanking is that you pull as much as you're confident you can survive (how much exactly depends on your gear and your healer's gear and ability but it's always more than one pack), go full AoE on your threat generation and let the DPS attack stuff in the order that makes the most sense for them. When things are starting to calm down you switch to MP/TP recovery so you're ready for the next pull. Since you're still a bit undergeared you may not be able to keep all mobs, but then it's the healer's and DPSs' job to handle that - quick is better than clean.

You'll notice that this means some of the things you did completely right during leveling now become completely wrong. Nothing will make your mates blow up like pulling one pack at a time and marking every mob. Even if you don't know the place, do pull at least 2 packs at once and try to keep aggro without marks. Even if you make a mistake people will be more inclined to forgive you if you showed the right attitude.