2003 Chevy Avalanche cylinder misfire

possible bad head gasket, bad injector wiring, bad PCM, bad plug wires, injectors need to be cleaned. Most likely a vaccum leak at the intake manifold. there can be a whole list of things. did you check to see if thre was spark at the plug wires and injector pulse at the fuel injectors. also check for a vaccum leak at that point of the intake