Welcome to the Forum from NH.
Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.
I hope that you will become a participating member in the Forum's discussions.
Pics of the truck, please.
On my 07 Yukon XL Denali when I had my Tech 2 bi-directional scanner connected to the GM module programming site, I noticed that there was a programming update that removed the auto lock feature. But, there was also a newer programming update that added the auto lock feature back. My guess is that was a transitional period where the auto lock was a 'feature' before it became a DOT requirement. You could check to see if this auto lock programming update is available for your year truck.
