[johnnyoro]

Hi there are probably no fault codes as you would be getting some sort of warning on the dash if there were
Get a cheap obd dongle and one of the phone apps and check yourself. I recommend carscanner
If there is no proof off gearbox oil change then get that done or do it yourself using pump and dump. I did mine at 42k and it made a huge difference.
Also change the fuel filter and fill it with injector cleaner as you refit it ,then 2 or 3 tankfuls of the expensive fuel as it could be something like fouled injectors