2 times now in 3 mths car had held on to the gear too long will this show up diagnost

My car 280cdi has for the 3rd time in 3 mths held on to aprox 4th gear right up and above 3000 rpm i tapped it down a gear and tapped back up to D again its going in next wed for a full diagnostics test and then a gearbox oil and filter flush and change ..

What i want to know is will the failing of changing up on those occasions show up in the diagnostics test ?.

Is there any way you can press the throttle that will make the car hold on to a gear ?.