My 2001 F-250 SD door lock actuators got so bad I went to using a key! I bought a pair of OEM actuators from:
http://www.commandoalarms.com/itm30005.htm and mounted them under the latch inside the door using screws supplied where the door starts to round up.
They fit nicely in this position but it does require forming a stiff piece of 1/8" push-pull wire with 90 degree bends to the hole in the latch where the old actuator arm was located. It took me a few hours of time but when I was done the lock actuators worked flawlessly using the existing 2 wires that went to the old actuators. Wire plug needed to be removed and end conneted to the new actuators that were installed. Two holes had to be drilled in the inside door metal to mount with screws supplied. stiff wire length was about 8" for each door. Be careful to route wires so the window does not lower onto them. position use tie wrop or tap to be safe.
The reason I went the OEM route was because of all the post on lock actuators in FTE. Not a job for the faint of heart but about the same difficulty as changing spark plugs on a 2001 F-250 SD 5.4 ltr. Hey it was almost fun again!