2001 Ford Cougar Speedo fault

Hello I have a problem that no seems to now how to sort it my cougar has a fault with the Speedo and mileage not working but rev counter works and not finding any faults when diagnostics done got to its wiring so had a auto election charge £60 to say was fine been told its gearbox sensor and told sendor in wheel so don't no where to go just using a app on my phone with GPS Speedo but no best at nite gets in way of view apparently it's common fault can. Anyone shed and light on this thanks in advance paul