Update with my sons RWD 2020 RST, He lifted his truck with SuperLifts 3 inch kit which includes rear Bilsteins shocks. And it has fixed the issue with his truck, he states a night and day difference for the better.
Bumping the thread, as I just bought a 2020 Trail Boss and I get the same sway but less now that I installed 295/70/18 and new wheels. My son just bought a RWD 2020 Silverado RST and it also sways? Anyone find out what's the issue?