2002 Chevy Cavalier Replace PCM/ECM?

My car setup is a 1600watt amp, 1400watt subwoofer, both tweeter and mid speakers aftermarket, cd deck and I also have 3 sets of LED lights that run 12volts each. My problem is that my dash monitor icons are lighting up (parking break/service engine/fluid is low/ABS/Car Alarm/Seat Belt) giving false readings and to make things worse my gauges drop to 0 that includes (RPM/Speed/Fuel/Engine heat level) when I press on the break and when I release they go back to normal Also my cd deck randomly turns off/on again. I went to a shop and got my battery/alternator tested and the volt meter said everything is fine with them and the problem maybe with my car computer. The mechanic asked me if I possible had a crossed wire when I wired the speakers/lights but I told him that I was very through and professional with the wiring in fact I checked the cd deck, LED lights and amp wiring which was correct and properly wrapped up. I think it maybe the alternator because for one it's stock same with the battery which means when I play my music the lights on the car dimm with the bass and with all the LED lights I have on as well doesnt help and I don't have a cap to aid the amp from preventing the dimming. But at the same time the alternator was tested and passed also the mechanic told me that if there was too much power drainage for the alternator it wouldn't run so that there cancels that out I guess. I'm doing some tests to try and narrow down the problem because just to run a diagnostic on the computer is gonna run me $110 I'm driving with my sound system, led lights, cd deck off to see if the icons still come up also I have ABS so I think when I press on the break all the gauges drop because of the power it takes to run the ABS or mabye it's just conflicting with the computer. Also when I turn off my car and restart it all the icons are off and the cd deck runs fine when I'm not driving only when I drive do the icons and cd deck start giving me issues. Can you please help me troubleshoot this and also can you give me a code number or anything regarding the computer chip just to see prices it's a 2002 Cavalier Manual.