There have been so many cylinder heads replaced on a 6.0 Powerstroke that a lot of parts have been mixed up which can and has caused problems. The biggest reported problem is if you are using the wrong injector clamps for the cylinder head. This can cause injector seals to blow out and can cause hydrolocking of the engine.
Use this chart to determine which injector clamp is to be used on which cylinder head based on the casting number on the cylinder head.
If there is no casting number, it is a cheap chinese head and you should scrap it because there is no fixing the problem.