I have an 05 LS V6 that is missfiring over 3500 RPM. Under 3500 the car runs fine and throws no codes, over 3500 I get P0300, P0301, P0302, and P0303.
I replaced the Plugs, coils, and wire harness to coil connectors.
I'm a a loss for what maybe causing this, but I remember reading somewhere...