2000 Ford Excursion Door Locks

The function of the door locks has steadily degraded. The driver's door was the only door we could unlock with the key fob a year ago. On a good day then we might be able to lock or unlock the rear tail gate. Now we are relegated to the key only. When inside the vehicle we can lock the driver and front passenger doors from their respective door lock switches but must lock or unlock the rear passenger doors manually. When the driver's door lock button is pushed the other door locks try to react but there doesn't seem to be enough 'umph'.

I have to get this straightened out - it is causing marital strife.

Thanks.