[HUF]

Start the engine, open the hood and lift the throttle lever up with a finger to increase RPM to some 3500-4000. Watch carefully for leaks. The plastic T (called heater valve) may leak UNDER PRESSURE. It is on top of the engine behind throttle body. Some connections, radiator side tanks, etc. are known sources of leaks as well.
I am pretty sure yo have got an external leak, leave the headgaskets alone for a while. The T is a very possible source of the leak taking into account your symptoms. The white smoke is the coolant hitting the hot exhaust manifolds.
I would also replace the radiator cap.