[Rigit1]

Just got new 2021 Duramax it seems to shut off after ideling for one hour.
is it in the programming is there a switch I missed?

I don't know how you're getting an hour. My 21 shuts down after 15 minutes if remote started and 30 if started by hand. On these late models there is no way to change the length of time or disable the feature. A work around is put on the emergency brake and put the truck in nuetral. I did this during a power failure during a winter storm. I needed the power for my cpap. In my case it's dangerous to not use it. Truck was in the garage on level ground so risk was nil. Burned better part of 1/4 tank in almost 7 hours.