I'm dungeon grinding and I'm also having a hard time, it's really slow. I'm considering tanking 2 characters and just level them up Questing and leave the other 3 behind.
I have a Rogue(My Main) in my group that is also slowing me down alot since I can't AoE farm at all, mobs are at 10-20% hp when my casters run out of mana so I guess if I had another mage/lock I could AoE farm and maybe it would be faster, but right now I have played very little the last 2 weeks because I'm a bit frustrated so I'm not really in the mood to play the same dungeon over and over again.

So I guess if you have a good AoE team you will level fast, if you don't have an optimal team its slow.

Any suggestions to not get burnt out? I thought about AoE grind non elites too but not sure how fast that would be or if my team is able to do it.