Shouldn't you have stepper.run() inside stepMotor() and nothing else.
stepper.runSpeed(); did the trick.
For testing purpose I just set maxTest to 100.
Motor runs and values of the force come in.
You seem to have chosen acceleration - that may interfere with what you are trying to do, take it out for now. And be sure to set the motor speed to match the step time that you want.
Acceleration line removed.
Thanks,
Paco