I picked up a new '21 Silverado RST a couple months ago. It has the 2.7 turbo. Mileage thru 2k miles so far is ok (18 mpg avg; best hwy so far - 25 mpg).
For me, the 2.7 has all the power I need. The low-end torque is great, and I've never had a problem passing anyone on the highway. The 8-speed has behaved fine and seems decently matched to the 2.7, at least in my personal experience so far. Time will tell if this powertrain holds up, but I am very happy thus far.
Pics attached. I replaced the oem antenna and added nerf bars & a tyger cover. So far, I love the truck!!