Truck rolls in park

[Redryan]

I have a 2018 2500 duramax. Live in colder climate 22 degrees today. Park on a 20degree ish angle in my driveway. Put truck in park. Rolls backwards by itself a couple feet at a time. This had happened a few different times all in the winter. Have not brought it in. Don’t have the money to pay for them to diagnose and not find anything wrong 

[swathdiver]

3 hours ago, Redryan said:

I have a 2018 2500 duramax. Live in colder climate 22 degrees today. Park on a 20degree ish angle in my driveway. Put truck in park. Rolls backwards by itself a couple feet at a time. This had happened a few different times all in the winter. Have not brought it in. Don’t have the money to pay for them to diagnose and not find anything wrong 

You are supposed to set the parking brake before you put the transmission into park.  By not doing so you have damaged the parking pawl inside the transmission.  If you are setting the brake and she's rolling, the parking brakes need to be adjusted.