How do I know if I need to change a regulator or motor in my window?

I have a 97 firebird with very low miles, but the windows continually stop working.They have gotten to where the will only roll down a tiny bit and once they do they take for ever to get back up. Like they have to build energy to do it. I assume that would be the motor, I replaced a motor (with another used one) and it soon died too. Why is it doing this?|||The switch could be shorting the motor