RE: 2004 silverado radio changeout
They say you need an interface for every new car these days. I went ahead and got one because I didn't want to chance messing anything up. I used PAC C2R-GM24 from e-bay for $80 shipped. they wanted $120 at the stereo store. You will lose the door chime for sure if you don't use this. I'm not sure what else will not work. I also got an interface that lets you keep your steering wheel controls, PAC SWI-PS. I haven't had any problems and everythingworks great. Easy to install.
I put a nice Pioneer with Blue tooth phone capablities, usb connection for a hard drive, ipod hook up, and Sirius. I have every feature thay my buddies new BMW has and I did it all for $500.
If you have any other stereo related questions let me know. I'm still in the proccess of hooking everything up, but I've had no problem figuring it out so far.