especially since one of my co-drivers rented a 2015 duramax and 2015 cummins and he was using 2.5 gallons of def every night, and so was my dad in his service truck,
I believe that is extreme circumstances. The average owner of an EcoD, Dmax, PStroke, or Cummins will never experience that high level DEF consumption.
I know. I was just trying to be funny. I used to drive a sprinter and Isuzu cube truck for work. I don't remember exactly how much def I used. Mostly because it wasn't me paying for it. But I don't remember it being as extreme as that.
One cool or irritating feature depending on how you look at it. Was the Isuzu, when it wanted to regen a light would pop up on the dash. Iirc you had about 200 miles to put it in park and press a button on the dash. The truck would automatically idle up. Like way up! For as long as it took to clean out the filter. Usually about 15 minutes.
You could interupt this if need be too. It was a pretty slick system.