[rhandwor]

I would first look over everything for something connected wrong. Then do a compression test a head gasket could have been put on wrong, wrong side turned wrong ect. Be very careful if tearing down to find the problem. Was everything torqued properly. Use a flashlight lay it flat along the block looking for cracks between the cylinders. Was the head pressure tested if not do this before putting back together. If two cylinders next to each other are low check closely for a crack between the cylinders.