Those are expensive repairs if you were to have to do them on their own and only on a 5 year old truck, I don't get people who say a vehicle is great in spite of needing expensive repairs at a young age and in my shop Duramax is king of expensive repairs.
The Duramax 3.0L diesel has a belt driven oil pump.
The oil pump belt needs to be replaced at 150,000 miles.
In order to access the belt - the transmission needs to be removed.
"Does the Chevy 3.0L Duramax diesel have a design flaw?"
https://pickuptrucktalk.com/2020/08/chevy-3-0l-duramax-diesel-design-flaw/"What you don't know about the 3.0-liter Duramax diesel":
https://www.youtube.com/watch?v=NFNsg7bCtdA&t=344s 
