My next step would be to get a test kit to check for exhaust gases in the coolant. You can get a loaner kit from Autozone or O'Reilys. You may have to purchase the testing fluid, around $7.00 if memory serves. Comes with instructions, and is very easy to do .... under 15 minutes.
These engines are known to blow head gaskets if they are overheated. Sometimes it will go bad on the first overheating, others will overheat several times, and not blow the head gasket. That appears to just be the luck of the draw, and how badly it overheated.
Once the head gasket is faulty, the engine will continue to overheat, even if all other cooling system components have been replaced, because the combustion gases are being forced into the coolant. The function of the head gasket is to seal the cylinder to the head, containing the igniting air/fuel mixtures pressure to force the piston down. The same gasket also seals the coolant passages in the block and head to each other, and the same for oil return from the head to the oil pan. Each of these three functions are isolated from each other, and a blown head gasket can get coolant into the oil which will appear "milky", oil into the coolant, or exhaust gases and pressure into one or both of those fluids.
That is about all I can offer on the subject, you appear to have eliminated the other possible causes like a stuck thermostat, partially plugged radiator, faulty pressure cap, damaged or broken water pump, or cooling fan not operating when it should. If all that is working, the head gasket is all that is left, assuming the block or head is not cracked.