Driver's side power window - Can't think of what to do.

My driver's side window, makes a squeal and then rolls down. Never a problem rolling up. Eventually the squealing lasts 60 sec and the window at the end grunts and goes down an inch. If I spend time trying to roll the window down, after maybe 25 trys on the switch it will roll down an inch. So I ordered a complete window kit with the regulator included and had it installed. Window exactly the same, no change. So I order a new switch and after installation, window exactly the same. If I spend a lot of time, I can get it to roll down still. After installing new parts, what could be the problem? Does anyone know?