Car and Driver got ahold of a 2020 new 3.0 diesel inline-6 Silverado and managed to squeeze 40.6 mpg out of it on the backroads of central Oregon. They I don't think say exactly if that was a crew cab 4x4 version but it looks yo be in the pictures. That's pretty respectable with also the ability to tow over 9000 pounds.
https://www.caranddriver.com/reviews...-diesel-drive/