suggest you change the stepper code to include a small delay
for(int i=0;i<steps;i++){
//loop through the number of steps that the stepper motor must complete
digitalWrite(stepperPin, LOW);
[glow]delayMicroseconds(500);[/glow]
digitalWrite(stepperPin, HIGH);
delayMicroseconds(1000);
}
and rather than sleep (to disable the stepper)
why not use the Enable input instead?