2024 2500hd Duramax High Country

2024 2500hd Duramax High Country. This is the first time i got a def message on the 2024, but i remember. Current truck is a 2014 duramax with the 6 speed.

Have always driven chevy from 1500 ltz, high country etc and 2500hd. Looking at a new 2024 at4 and just curious if the 10 speed transmission helps with mpg.