[hdrolling]

I also have an '18 Duramax, your good to wait until your DIC says it's time to change your oil. You'll also get a message from onstar via email, not every truck is worked the same so not every truck needs to change it's fluids at the same mileage.


On the L5P engine GM recommends not using additives like the previous years engines.


As far a the DEF fluid, I wouldn't worry about going bad in your truck just don't store old DEF in your garage and try to use it after it's been open a year later.

Dealerships have loads of truck that don't sell for a year or more that might never get driven and I'm sure when they do sell them they don't drain the DEF and fill it with new.