A:AnswerYup it’l work. I purchased that one for my 2003 silverado and I’ve seen 2006 silverados with still the same harness adapter so your 2004 one will work with this one
A:AnswerYes but if you have a factory subwoofer and amplifier you will need to bypass them with the following additional harnesses: Metra 70-2002 and Metra 71-2002. You will need to disassemble them and move wires around to different pins in the harness. A paper clip will work but after doing this myself I recommend a pin removal tool as it will make it easier. Here is a link to the step by step process. http://www.savagehomeautomation.com/projects/bypass-factory-ampcrossover-in-2002-chevy-tahoe.html . If you do not have a factory sub then ignore this extra information.