Ford Futura software issue

My 2008 Ford Futura BF MK2 has only travelled 56,000 and is in new condition, but there is a problem that has been niggling me for the last two years. As I am driving along in a 70 km/h zone or over 60 km/h zone I get up to around 77/79 km/h and any reason have to feather the throttle, the transmission "thumps" in very hard, quite a bad sound. While driving normally and approaching 80 km/h the transmission moves into fifth with "reasonable" smoothness. My wife has the same model station wagon and that changes much more smoothly. The dealer tells me it is ok, but I am concerned that some damage is being done and I could end up paying for the "repair" when my extended warranty runs out. Is this is an existing "known" problem with the BF transmission.