I recently changed my head gasket on my 4.0. After buttoning it all back up, it had an extremly rough idle and the cel came on with code 12 and 21. The wires going to my 02 were fried so i repaird that and did a good check for vaccum leaks. Now it is getting code 12 and getting 21 twice. It has an extreme lack of power under a load. If i mash the throttle it will not respond and is vey sluggish. Any ideas or input is appreciated.