Arduino, Nema 23 Stepper Motor and TB6600 Set up problems


I’m having trouble with setting the $100 $101 $102 values on the Arduino to match up with my motors steps per revolution.

I have Four NEMA 23 motors:
Shaft Size: 1/4"
Step Angle: 1.8
Holding Torque: 1.26N.m
Rated voltage: 3.36V
Rated current: 2.8A

I have done the calculations:
lead screw is 2mm pitch, 8mm lead, 4 start.

200 Steps per rev x 8 Micro stepping = 1600 steps per rev
With 8mm pitch
1600 steps per rev / 8mm pitch = 200

Yet when I enter $100=200 and tell the machine to move 100mm it moves 200mm instead. So I have set the value $100=100 which moves the correct distance.

I’m using a TB6600 driver at 2.0A instead of the 2.8A the Nema 23 requires because it runs slowly at 2.8A?

My connections from the driver to Arduino are:
PUL+ TO PIN 2 (On the Arduino)
DIR+ TO PIN 5 (On the Arduino)
PUL- TO GND (On the Arduino)
DIR- TO GND (On the Arduino)

I am using GRBL on the Arduino if that makes any difference.

Is there something that I have done incorrectly or any values that I need to change in the Arduino?

Thank You.