Apologies for reviving this old thread :) GM uses this stupid wax coating on their frames. Of course it doesn't stay on the frames, so they start to rust. Not only that, when the wax starts to pull away water/dirt/salt/etc can get in behind the wax that remains, so it'll rust but you won't see it.
I currently have a 2019 Silverado, with the 5.3L. It's mostly OK (I don't even mind the interior), except for towing - several times while towing our travel trailer (6896 lbs, 806 lb hitch weight), the transmission has overheated. The truck is rated to tow 9500 lbs, with 1767 lbs of payload...