I’m new to GM and this forum because I’m considering ordering a 2021 Sierra Denali. After reading the first 20 and last 20 pages of this thread, I’m shocked to see this problem continue through 3 model years. It seems the only solution is to order a truck with a solid rear window, which is possible on some models, but not the Denali. I may try to get a sliding rear window delete on my Denali order, but if not allowed, then I may order the SLT with solid rear window. Or I may just go with a Ram 1500. Very disappointing because I had my heart set on the Denali.