You going to have to buy a RCA adapter for your stock tuner, all GM radios have the auxiliary audio input. The problem is that the wiring and module is not in the vehicle, this port was there for the rear dvd system and you can plug this into the 12 pin plug on the back of the radio use this http://www.oemautosound.com/c-87-gmc-auxiliary-input-converters.aspx
Good luck and just order the PIE GM12-AUXv2 GM 2002-2008 Auxiliary input adapter