The ford fiesta and ford focus both suffer from TCM (transmission control module) failures, these are not uncommon and are a recognised problem in ford vehicles. The transmission ECU (TCM) is very easy to remove and replace but also its very expensive, From your ford main dealer you will be looking at £900 upwards depending upon the part number you have.
Check out a short VLOG update featuring the ford TCM that visited us,
The part number that we have replaced is a2c30743100 although its ford branded it is manufactured by continental. The TCM will need to be programmed to the vehicle and then you must perform a relearn of the shifter and the clutch as well as clear all adaptations. As we are Ford specialists we have ford IDS (main dealer equipment) that allows us to independently programme and code the TCM.
The common reasons and symptoms for replacement are communication errors stored in the ecu along with poor / harsh gears changes and throwing out of gear when decelerating.