For those of you who are looking for a really easy and painless way to blast through those last five levels, here's a video showing you the darkhold mass pull kill method people have been using:
http://youtu.be/dsn1uvVtsAU
It's super easy and works with any regular 4 man set up. It is slightly faster with 2x casters but definitely works with 2x melee as well.
Enjoy!