I have a 2021 AT4 with the 3.0 that i've had since late 2020. It currently has ~ 72k of reliable operation with just normal maintenance (Oil/Air/Fuel filter changes) when the computer calculates 15-20% life remaining. DEF really hasn't been an issue, the 5 gallon tank only needs to be filled every 4000 to 5000 miles and with gas stations starting to install bulk DEF dispensers at the pump it's been increasingly easy to keep up with. Changing the oil, air and fuel filter is a breeze. I order them off of Amazon and i can change them all in a single service in less than an hour.
Mine typically makes 5 - 20 mile trips, not sure if that qualifies as grocery getter mileage but so far i haven't had any issues. I do feed it quite a few of the Lucas Oil products (Deep Clean, Oil and Fuel Additives) because i have a buddy that is a representative that gives me some samples (BTW, the Lucas Oil Diesel Anti-Gel works very well).
After 4 years and 70k+ miles getting a combined City/Hwy mileage of ~24 mpg i'd be happy to recommend the 3.0 Duramax for half ton applications.