you need the head skimmed otherwise its just going to cause more problems with the engine. the
garage should have had the head skimmed. sounds to me the
garage cut a lot of corners of the rebuild i would not be surprised if they did not even fit new valve seals. there are some that think of cheating by not skimming the cylinder head saves time and the hassle of stripping out the camshaft bearng caps the hydraulic tappets camshafts. than getting a valve spring compressor taking out the valves checking the valves for damage and then if they only need a clean cleaning the valves of carbon makes fueling and compression and fitting new valve stem oil seal on the valves better is too much work.
the
garage should do all the work again and skim the head all free of charge.....