When I hit the unlock button the driver door will unlock, the passenger door will unlock 80% of the time, the rear door behind driver will unlock 50% of the time and the rear passenger door has stopped unlocking all together. If the unlock button is hit several times it sounds as if the power is going out.
Anyone know what the problem is and how I can fix it?

 

Perhaps it's just sticky and needs some cleaning and lubrication? Remove the door trim panel, clean it and lubricate with WD40, once it's moving normally and is well lubricated, then you need to spray it with white lithium grease as the WD40 won't stay for long.

 

Since all doors locks are working it is not an electrical problem. The electric lock motors in each door could be worn or just in need of lubrication.

 

Here's a very lengthy post on the thermistor problem. These are a temperature resistor, installed to avoid overheating and potential fires when the lock/unlock buttons are pressed for a abnormally long time. They eventually fail and won't provide enough current to activate the lock mechanism.
This thread refers to Super Duty's but the Expy door actuators come apart a bit differently but it's all the same issue.
Enjoy the reading.

https://www.ford-trucks.com/forums/4...cks-fixed.html