I hope you guys are not operating under the assumption that the "Truck and SUV" oil is the same as Delvac 1. Delvac 1 is formulated for diesels with added detergents for soot dispersal. The T/SUV is formulated for gas engines and most likely a microscopic if any difference between it and any other Mobil synthetic oil that is formulated for gas engines. Almost all oils developed for gas engines will have a C rating, but it will be an aged C rating and does not have the added detergents that a diesel really needs.

To know for sure look at the Mobil Delvac or Shell Rotella T container for the highest C rating which I THINK is C J4. If the T/SUV oil does not have that C rating it is not what's best for your diesel.

The Truck/SUV, high mileage, etc are simply slight variations or maybe just a different weight of the companies standard oils, but packaged to create a market. Labeling oil in such a way, makes it easy for the average person to choose an oil. They think wow I have a truck, or I have an SUV, this is what I'm supposed to use. From a marketing standpoint, it's actually quite brilliant.

For your diesel, make sure you select an oil with the LATEST C (compression ignited) certification.

Have a great day,