Motor heating when "not in use" - steppers aren't quite like other motors. They take power to hold position even when not moving. What the driver will probably let you do (it's often a DIP switch setting) is reduce power to half while the motor is stationary. I think my drivers do this if the motor has been stopped for more than a half-second or so. That might help if you haven't selected this already. Seems normal for steppers to run hot anyway - too hot to touch but not hot enough that a drop of spit sizzles seems ok...