For the third time, my Chevy Traverse's transmission failed to engage into drive after placing the car in P (park).

On a long intersection light I placed the car in P. When the light turned green I immediately placed the car in D and made sure it was in D but it did not drive and had a transmission slippage of some sort. After a bit it seemed to decide to participate and then I was able to drive. It was scary as the car behind me almost rear-ended me since I didn't have a break light on as I was hitting the gas pedal.

This problem occurs when I place the car in P(park) on long stops like for waiting on a train or drive through.