How can I fix my Nissan Primera CVT Gearbox?

My 1997 Nissan Primera has an intermittent fault where its changes gear down when it shouldn't, e.g doing 100kms on a motorway it spontaneosuly starts to chop down. The only way to fix it is to come to a complete stop and turn off car and wait 5 mins and then restart. Relatively new car only done 130,000 kms.

Fault may occur 10x per day or not at all for several days but seems to be getting more frequent. When car is turned back on CVT light may be flashing, Revs also increase as the car is changing down. Sometimes car is also revving whilst driving for no apparent reason

Have replaced gearbox computer, gearbox sensor, stepper motor, also had full transmission service. All done professionally.