2004 Chevrolet Colorado, Stereo Install

I had cheap Chinese stereo in this car and it always powered up with the display on, but some days there would be sound, and other times no sound. So I replaced the stereo and with a cheap one from amazon, and still no sound (It lights up just fine). I am using a GMRC-01 Chime Interface (No OnStar) so was wondering if there is an issue with that. So I replaced the GMRC 01 Interface, and install a JVC KW-M560BT stereo. Start the vehicle up and again, there is no sound. Next I checked the integrity of the factory harness to the individual speakers. I have four speakers in the vehicle and there are 8 leads in the factory harness (a positive and a neg for each speaker). So I put 12v on the positive and ground the negative for about a half second on each speaker and they all pop as expected. Next I connect a piece of the speaker wire to spare speaker I have lying around, and the other end to the speaker output of the new jvc stereo. I tried each of the gray, green, Purple and white coming out of the ISO harness out of the back of the stereo. No sound at all. Next I connected the blue antenna wire out of the stereo to the Interface. That didnt help either. Next I try putting the leads into the rca plugs for speakers out. When I do that, I get really low sound out of the speaker, but I can hear it. I dont think this Colorado has a factory amplifier, but I am wondering if it might. If it does have a factory amp, any idea where it might be located? I am at my wits end on this thing. I tried 2 new head units, and one new interface, and I still get no sound. Any idea what to try next?