It looks like you have the scaling not set properly,
[AXIS_X]
MIN_LIMIT = -1000.0
MAX_LIMIT = 1000.0
MAX_VELOCITY = 100
MAX_ACCELERATION = 5000.0
[JOINT_0]
TYPE = LINEAR
HOME = 0.000
MAX_VELOCITY = 100
# NOTE: the step generator module applies its own limits to
# acceleration and velocity. We have discovered that it needs
# to have a little "headroom" over the accel by the trajectory
# planner, otherwise it can fall slightly behind during accel
# and later overshoot as it catches up. In the long term we
# hope to come up with a clean fix for this problem. In the
# meantime, please set STEPGEN_MAXACCEL below to a few percent
# higher than the regular acceleration limit MAX_ACCELERATION
MAX_ACCELERATION = 5000.0
STEPGEN_MAXACCEL = 5200.0
BACKLASH = 0.000
SCALE = 6.6666 <=============
OUTPUT_SCALE = 1.000
MIN_LIMIT = -1000.0
MAX_LIMIT = 1000.0
FERROR = 1.270
MIN_FERROR = 0.254
HOME_OFFSET = 0.0
HOME_SEARCH_VEL = 0.0
HOME_LATCH_VEL = 0.0
HOME_USE_INDEX = NO
HOME_IGNORE_LIMITS = NO
Have a look, you need the drive microsteping, pulley ratio if any, ballsrew pitch, to calculate that.