I’ve never noticed if all the NNBS GM full size SUV have the diversity antenna in the passenger side cargo area window glass or if every model uses them.
I do know there’s an antenna module that is connected to the roof fin antenna and the diversity antenna in the rear glass. When modules die, one or all of the frequency bands will fail.
Adding another antenna is a simple fix vs. hunting down and replacing the diversity antenna module that’s there to find the strongest signal in both antennas and prioritize it.
@iggy913 is looking for a 12-14 replacement head unit if you need a new home for it.