The power vent windows on my 01 Excursion have the same problem. After troubleshooting the problem, I determined that the vent motors were getting voltage to them although the voltage is somewhat less than battery voltage - around 11.5 volts to the best of my memory. (I had someone push the switches while I stood at the at the rear of the truck and measured the voltage). I also made another discovery while doing this, when the switches were pushed, I heard the motors make a "clicking" sound like they were trying to turn. I never heard this when I was pushing the switches at the front of the cab. I then determined that if I had someone keep hitting the switches in rapid succession to open the vents while I twisted the (rotating) arm that attaches to the window, I could free up the window and they would work for a while until they got stuck again. When they get stuck, I go through the same routine to free them up. I believe Ford has a faulty design in this circuit, they either have too much resistance in the circuit supplying the motors or the motors do not have enough torque to open the windows if the motors are supposed to work with only 11.5 volts. | 
