Less than 200 miles and the new AT4 is going in the shop...
Got in the truck yesterday, started it up, put in reverse and it would not move. It seemed as if the electronic e-brake was on, but the PARK light was not lit. Put it in park and hit the e-brake button, then the PARK light came on and started flashing and I got a message stating "Service Parking Brake", wonderful.
Turned car off, started back up, no more warning message and I was able to turn off the e-brake and reverse out of garage. Shortly there after I received two Onstar notifications, "issue with the StabiliTrak® stability control system" and "issue with the Antilock Braking System in your 2020 GMC Sierra has been detected".
The truck seems to drive okay, however I did notice some sort of clunking noise occasionally towards the back end, not sure if that's normal. Frustrating as I have barely even driven the damn thing since the dealer dropped it off new. It's going in for service this coming week. These issues seem somewhat similar to the past recall in the 2019s, although my vehicle says no recalls.