Dps are impatient and they don't want to wait 5 minutes between every single mob and end up having a 45 minute low level dungeon.

1) Stop marking. Tomahawk a mob, group them up, overpower 2-3 times, use enmity combo on mobs that are taking the most damage. You can hold aggro even if both dps are attacking different things. Just alternate your enmity combo after some overpowers. Do this and you'll never lose aggro unless your gear sucks. Don't have sucky gear.

2) Don't be a slowpoke. Don't over think your job. All you have to do is group mobs up and overpower/flash and then use comboed skull sunder/butchers block. Just go in and do it, you're healer will keep you alive. Stop waiting for like 5 minutes between each mob so you can prepare mentally for what lies ahead.

You're the leader of your group as a tank and you should play with the mentality that you're the best player in the instance. If you cannot do that then maybe tanking is not for you.