You can clearly see head gasket/surface issues with 4 and 6. Your head gasket is not sealing--end of story. Get your heads resurfaced by someone with a PCD cutter on a resurfacing mill and use some Victor nitroseal gaskets #5961. Clean everything up and reassemble--get a proven torque sequence and follow it closely. Your engine will be back to normal. Take a compression test before re-installing the manifold so that if it is a valve sealing issue you have one less thing to tear back apart. Or have the heads gone through before reassembling. Happy Motoring. J.Rob