This often happens when the car is still rolling backward and if the transmission were to engage it may cause some issues. (Not saying if this is to happen once or twice the transmission would be shot, but over the lifetime of the car repeatedly doing this maneuvered can be damaging). Therefore Chrysler allows the transmission to stall and hesitate until a more appropriate time to engage. I hope this is the issue and a quick resolution as it is hard to tell from the few details.