take a very carefull look at the rear side lights & brake lights and indicators to make sure the bulbs are 100% correct and there is no interference with any bulbs when barke lights come on or indicators flashing.

Corroded earths and corroded bulb holders or bad earths play havoc with the autoboxes.

very briefly the autobox is ECU controlled and if it gets a signal from the brake lights , often caused by a poor earth or incorrect or defective bulb it puts the box into a default mode & it wont change gear !