See you live in WA. DEF might be an issue if you go up into the mountains. It gets colder up there and around here and the Dakotas, DEF freezing is a big issue with the newer diesel trucks during the winter months. If you live in an area where the temps get much below freezing for any length of time, it may not start or it may go into limp mode. I'd check on some forums to see if the Chevy/GMC is one of the new ones with the DEF tank heater not being able to properly heat up the fluid in the winter months.
I live at 7650 ft elevation wher it isn't uncommon fro temps go to zero or lower.I don't know if the smaller diesels are the same,but mu 2019 Chevy Duramx ,
10 cyl has no trouble with the DEF in regards to freezing,starting and running. The Def Tank has heater in it,but only when the truck is running
