Just wondering in past years if you are coming to a complete stop when shifting from reverse to drive or doing it as the car is still rolling. And vise versa. My wife is aware of that when she uses her Terrain or others over the years. Just my thought using auto xmissions.
Usually it's a low/worn fluid issue. If you haven't had your fluid changed by now, you might have damaged the trans. But fluid and filter should help. And it's not a warranty item as it is considered maintenance. Dont let them flush it as part of the change!