Ive used/have personal experience with MANY different GM factory radio aux input adapters, and ipod integration kits. USA-Spec, PAC, Axxess, iSimple, Denison, etc.... Ive used basically all of the available aux/ipod integration kits out there for the GM trucks/SUV's.
This one is BY FAR...HANDS DOWN...the best. You can keep factory XM, stream audio over bluetooth, bluetooth phone, shows title/artist info over the factory radio display, you can search for songs using the menu buttons on the factory radio...and in addition to the USB plug (for ipod or android phone), it ALSO has a regular 1/8" stereo input for DVD player, or an older phone that doesnt support the fancy USB stuff.
You can even use Pandora over bluetooth with it. And if you want to skip to the next Pandora song or station, you can do that all with the steering wheel controls or factory radio controls. The bluetooh pairing is perfect and works every time. You jump in the truck, start it up, and 5 seconds later it automatically starts playing music from your Ipod/Iphone/Android/whatever. The integration is flawless, and its very intuitive/easy to use too.
http://www.autotoys.com/x/product.php?productid=26516
Like I said...I have experience with lots of different factory radio aux input adapters....and this one ^ kicks all the other ones' asses.
note....the link I posted is for the GMT-800 class 2 databus radios. (03-07 classic) They make the same adapter/same functionality for the 07.5+ GMLAN radios, but obviously its a different part number.
ben