It appears both GM and FCA use the same two vendors suppliers for their rear sliders and both are having issues with leaks. All issues seem to stem from the cab flex and causing the frame on the windows to crack.
What's interesting is on GM forums, their was an initial TSB regarding the rear window leak assuming it was caused by not enough sealant applied during manufacture, which the fix was to apply more sealant. However it could come back a few weeks later after repair and seems to be caused by frame cracks.
Considering they are just figuring this out now, along with what appears to be similar incidents for RAM owners (though not at the same frequency) as there is a giant 78 pg thread about this issue at GM forums for 2019-2020 trucks, even though the RAM DT has been out a lot longer. It wouldn't surprise me that they haven't redesigned the window yet.