Intermitant slippage

Firstly welcome to the club hope we can help. Depending on age mileage servicing etc try changing ato trans fluid first if not a code read might show up a problem which could be internal (to the gearbox).

The mostlikely fix for this would be to have the transmission software upgrade installed , you will have to see the dealer for this . Mister T.

Check the level of your auto trans fluid. Too little fluid, even by a small amount, can create the symptoms you mention.