Ford Falcon gear changing

I have just bought an ex-police 2009 Falcon five-speed auto, which had 50,000 km on it when I bought it and now has 53,000 km. It was fine in the beginning, but gear changes are now sometimes clunky, especially going from second to third under 2000 revs. I believe it is still under factory warranty and when I took it to a Ford dealer I was told there was no problem. I know the gear change is not normal because I have driven a few different cars. I have read that police cars may require gearbox oil changes. I don't want to keep driving the car the way it is because it might get worse. What should I do?