I rode in my wife's 2006 Buick last night and noticed something curious. The stock Delco switches from 106.9 to 107.5, and back again according to signal strength. I was wondering just how that is accomplished - it has to be something to do with RDS because the radio is not HD. Seems like a feature that would be more useful in Europe where a lot of stations are controlled by the government and simulcast.
There is a bit of synchronization problem between the two stations - it got annoying as it switched back and forth.