DirtyD'sSS

I really need some advice. I've got a 99 SS that's throwing low voltage, and knock sensor codes. I've had the computer refreshed within the last two weeks with little help. When I shift gears the lights blink and the voltage gauge moves a little. The car feels that something is holding it back when giving it gas then clears out after a few seconds. I've replace the battery and alt., along with plugs, plug wires, fuel filter, and both front O2's. The cats where knocked out and I've had a fuel pressure test done. The alt. was bumpt up to 160v and was tested before going back in. The car has no problem starting or staying running. A few of my buddy's think I may have a ground wire fault, but don't know how to go about finding it. Any idea????