Ya, totally agree with MPG's on the 3.0L. Guy at dealership told me a guy he knew did test run on one in Oregon with mirrors folded in and went 55 to 60 and achieved over 40 MPG's.
I do miss my 2018 MPGs. That truck just got excellent FE, but the 8 spd drove me nuts with it's 1st and 2nd gear clunking and hard shifting. I had it in the shop for GM to look over 5 times. They reprogrammed it, but refused to change fluid in it, said it was normal??, so I traded it for the left over 2019. This new 2019 is super smooth and it's finally getting decent mileage compared to what I was getting when I first bought it. It was around 17 mpgs. Was very disappointed in it. At first this has been the only truck I felt guilty buying because I truly loved the 2018 in every way except for that dang clunking/hard shifting.
Now, I am glad I switched, because these T1's are so much nicer, roomier, and livable then the K2's.
Again, either engine, you can't go wrong with in my opinion!