Kelly Ricard

Why does hill assist go on driving on level ground in my 2017 sierra Duramax 4X4 denali. Nothing shows up on the code reader. Ran diagnostic with Onstar while happening and nothing showed up there either. Dealer cant figure it out. It raises the idle about 500rpms and stays on at a dead stop. Even after I stop and start up again it goes on. Of course when I take to the dealer, it doesn't act up. Any thoughts