Can't get my iPhone 4s to play music in my Chevy Suburban factory radio

I have a 2011 Chevrolet Suburban and with my iPhone 3gs I could plug it into the USB port in the center console and charge the battery, listen to music from my iPhone, and control the music using the factory radio to access playlists, albums, artists, songs, etc. Now that I've upgraded to the iPhone 4s, it no longer works. When I plug in the iPhone 4s it will start charging the iPhone but the iPhone won't show up in the radio AUX section as available to listen to music like it did with my iPhone 3gs. Does anyone know if the iPhone 4 or iPhone 4s is still compatible with the GM Chevrolet factory radios (Tahoe, Suburban, Yukon, Escalade, etc.)? Is this a Chevy problem that can be fixed, an Apple problem that can be fixed, or an incompatibility issue that can't be fixed?

Thanks,

DK