Automatic kickdown problem

Good day
Toyota replaced the kickdown cable because they could not get the adjustment to work.
The first two kickdown work fine and the third time most times.
However when the car is hot the third kickdown does not work properly. All of a sudden out of its own it will fail and the revs will shoot up to 4500 about at 120km/h. Normally it is 2500 at 120km/h. Have been adjusting the cable anticlockwise.
The carburettor cable is rather loose but no adjustment has been made there.
I am a pen pusher so don't know much.
Any suggestions?
Toyota have just made cursory adjustment but the problem is not solved. Help!