Missing under a load

My 2000 focus zx3 standard started missing when I would first take off or right after I would shift gears (under a load). It acts like the electrical system is shutting it down. At first I thought it was the throttle position sensor because it would act up (stumble) when I would give it the gas. If I move the gas peddle slowly it will rev up fine. The speedometer bounces around crazy when it acts up and I can hear a popping sound in the speakers. I had a new sound system and alarm system installed about two weeks prior to my problem. I brough it to the ford dealership and they could not fix it and suggested that I bring it back to the audio installer. I did this and they rechecked all the ground wiring and said that they use their own grounds and everything looks good on their end. No check engine light is on. I pulled the wire off the TPS to see if it would run any different and it did so I guess its ok. The check engine light did come on at this point and autozone confimed that when they plugged in. I bought a new battery (675amp), plugs and wires, and fuel filter and it has helped a lot but the problem is still there. Should I replace the coil and TPS anyway? One autozone employee told me that I needed a 1000amp battery because of the ampifiers in my car. Any truth to that? Also I just noticed that when the engine is under a load it pings and maybe a knock sensor is shutting things down. Anyone have any thoughts.