I use my 2020 Trail Boss truck for pulling my RV and I love this truck, just found out I was having this issue of leaking back window, I took it in to the dealership and found that my extended warranty doesn't cover water leaks or bad seals lol wtf (don't buy the ext warranty) it doeasn't cover ******. anyhow was told to fix this it would cost $1,265.00 so it has to be fixed so in the meantime I contacted GM they are looking into it and will tell me in a couple days what they can do for me I will post the results of this seeing how this is a manufacturer issue, my truck only has 17,600 miles on it.