Hi Steve...welcome to the Forum
I would say it is more than likely a sensor issue or even damaged wiring or connector going to the sensor.
One other thing you could try first is to remove the battery negative terminal and leave disconnected for an hour or so, then reconnect and shift the gears slowly but repeatedly backwards and forwards (low to high and back again) whilst stationary with the engine running and handbrake on so the control unit can relearn the gear positions.then take it for a drive to see how it works. Done that one a few cars (other makes) before and it tends to work, but worth a try if nothing else before committing to spending money on parts, etc.