This exploit is based around level(s) 47-54, and its about speed running through nightmare Azmodan and the trash before him.
I did this as a wizard and leveled from 52-55 within 1 hour and 30 minutes. Also got about 150k gold within that time from just doing this.
Act 3 part 7, Heart of sin - Kill Azmodan.
1.) Take teleport to where you are supposed to go(you will spawn right next to portal when you enter game)
2.) Speed run through the trash, I did this easily at level 52 with about 4k damage and 6k health.
3.) Go into Azmodan's lair, engage him and stand behind the pillar in the middle to avoid his fire balls, when he got close enough I used Archon ability and just beamed him down within 15 seconds.
4.) Collects your rares/blues and teleport back, take next quests from the quest giver called liuetenant or something, run into armory and up to the tower, and there you go. You just completed 2 quests.
This run should take you about 3-5 minutes, and you'll get 4-5k gold each run, aswell as about 100k~ exp
This is a powerleveling method, which was being used by players such as Athene who got about 200k exp each run since he had extra exp gain.