From my past experience as a automotive machinist, it's a hit/miss to be able to repair a head gasket related problem by simply replacing the head gasket. Once the surface of the head and/or block is less than perfect, a new head gasket may or may not fix the problem... it may temporarily band-aid the issue, but if there's erosion, warpage, or even cracks, in the head or block... you'll need to invest more than just a new head gasket to make a good repair.
When the head was off, did they pressure test it by chance?