I had the rear power window motor replaced on mine a 20K. I haven't had a problem since. I did have problems from brand new until it finally quit all together, luckily the window was closed when it crapped out. The dealer had the motor changed in less than two hours. Good luck!

 

My power slider has quit working also. today i took the back seat apart and got to the motor. i tested the wires they were switching polarity like they should be when the switch is pressed so its the motor that has siezed up on mine its most likely the sitiuation with yours. Mine was intermittant before it all out quit

 

With all of the problems that i have read on this forum about the power slider Just take a couple of minutes and open and close it I rarley use mine but i open and close mine every day

 

That seems to be the key to keep them working. i called the ford house and they want $153 and some change so when i get the new one ill make sure that i use it every day or so just to keep it working