Okay I've just done a quick search, have you tried these settings in the firmware/app? >
Change "X and Y max acceleration" from 1,000 to 750
Change "X and Y max speed change" from 15 to 6
Change "Right and Left extruder max acceleration" from 2,000 to 1,000
Change "Right and Left extruder max speed change" from 20 to 10
High acceleration is a key issue according to many users testimonies I've read, as well as not enough belt tension.