There's an exploit in act 1, rumford at the gate, where you kill 2 wretched mothers on normal, (teleport to town) log out, change difficulty from normal to torment 6, then log back in and and attract last wretched mother to the town gate, where she will be insta killed, resulting ~450m xp/ 3,6m gold in an hour.
VIDEO LINK OF THE RUN! https://www.youtube.com/watch?v=Npw6IPQQqCo