Thanks for the reply.
Something to consider. If you are out of any warranty period, you will be paying the dealer a high hourly rate for an often substandard mechanic to work on your car.
The "couldn't find an issue" is so common, that I am no longer surprised.
If you can find a workshop with older experienced mechanics you will better placed.
The speedo reading is coming from wheel and differential speed sensors. They also give traction control info.(ESP)
The rev counter works on a sensor in the motor.
They obviously dont all fail at once, but their inputs are used in the (ECU) main computer. That is the logical place to look.
Connectors to it or internal component failure. Doubt program failure but could be.
I assume there are no codes???????????. If ECU goes down it probably cant record a code.
Good Luck.