You need to run a cooling system pressure test. Your tractor shows all the symptoms of a blown head gasket. Yes, I know the head gasket has been replaced and I presume the warped head was milled. That doesn't mean it's OK now.
The typical way to check for a blown head gasket is to attach a pressure tester to the radiator and fire up the engine. If the pressure immediately skyrockets, you have a blown gasket or possibly a cracked head. (Turn off the engine quickly so you don't build up more pressure than the cooling system can handle.)