I left the GM delership service buisness two years ago (after 26 years ) and maybe they fixed the problems with theire diesel. I need trucks todo heavy work and towing. We use mostly 450 auto and have very good luck. They ride like trucks and don't get the best fuel mileage but they seem to last.
If I want a truck that rides like a big car and gets the best fuel mileage I might get a GM diesel and drive it like a car for 200,000 miles. And I do my truck is a 93 K1500 4WD but it's a gas with 135,000 miles but I drive it like a car and it's great for me.
But I don't think the GM Diesels in a work enviroment will last as long as the Fords would, and that is from my exp. in the GM service buisness.
But I do like my VW golf diesel 245,000 it has an oil leak from the headgasket but what do you want for 245,000 miles!