You won't get anything like reasonable performance from a stepper if you don't ramp the speed up and
down. Try using AccelStepper library.
You must set the current correctly on the driver - too much and something will cook and fail, too little
and you'll get less performance. 1.8A is beyond an A4988's range which won't help.
Make sure you've correctly identified the two windings and connected correctly. Never disconnect/reconnect
motor windings to a stepper driver when it is powered up, you'll probably instantly destroy the driver if
you do.
The torque rating for steppers normally given is the pull-out torque (when stationary). Dynamic torque
can be much less, and depends on speed. Resonance issues dominate stepper behaviour unless you
use a reasonable microstepping ratio or mechanical damping.