Replaced a head on mine, vavle seats were bad stock motor. Had low compression on that cylinder. What did you plugs look like? I would't think you have a bad head gasket not very commonon these. Did the truck sit for a while?
Do a leak down test so you know whether its valves leaking, intake or exhaust. or rings, pistons. Bad valves are a very common issue with '04.'05 motors. Been there done that.
Hope I am wrong and it's something simple..