I recently replaced the 'driver side window motor master switch'.

A power window regulator is what connects or transfers the power of the window motor to move the glass up and down inside guides or channels. Often the regulator especially cable type as a cable wears can fray and start dragging and binding causing the motor to slow or stop and can eventually over load and cause a motor to fail. Operating an motor over loaded can sometimes also damage the controls like switches, relays, fuses or modules(most common types are Gear, the oldest, a flat nylon tape type used for a few years on GMs and the most common currently cable type which is much lighter and quieter the the original gear types. Other causes of glass moving slow/binding are when the channels/guides felt/rubber is worn, dry/damaged or bent. Cable regulators can also break which will often cause the glass not to go up and sometimes even fall and can hear the motor running when switch is pressed. I hope this helps, Jim CarMasters Automotive.