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