Overheat, excessive preasure build up in cooling system

Most modern engines have a degassing facility and sometimes those small ports and hoses block with silt and the small amounts of gas the head gasket has failed to seal will build up in the cooling system, displace coolant and perhaps disrupt the proper operation of the thermostat. Degassing is required to allow the gas to escape harmlessly to the space above the coolant where it eventually vents.

When a failing head gasket allows too much gas to pass into the cooling system even the degassing won't be sufficient and the thermostat operation is likely to be affected causing overheating and excess coolant displacement.

My thought in response to you mentioning trapped "air".

Let's start with the simple and make sure the coolant mixture was 50/50 and not 100% coolant. That will make it overheat.
Second, thing I would check is if there's a code for your catalytic converter or oxygen sensor. If your converter is clogged, then it builds back pressure that overheats the engine.
Hopefully that helps. That's all I can think about without actually having done the head gasket replacement myself or having inspected the vehicle. And make sure the heads were resurfaced and inspected as well.

Have you tried a new thermostat? It might be occasionally sticking closed.

Was the engine overheating before you replaced the thermostat ?
By not putting the cap on tight, you are not allowing the cooling system to build up pressure. So it could be a restriction somewhere like a radiator hose.

first thing i would have my pressure cap tested next i would pressure test the cooling system .you might have a blown head gasket near a watter gallery this will cause pressure in the cooling system.

Yes this could be a hose, a heaterhose, fill the cooling system and run the engine so that preasure build then before it gets hot shut it down and look for mhoses and squeeze them and try to locate coolant coming out , a preasure tester would be a great tool to find this leak but by you squeezing the hoses you should find the leak or even when the engine runs it may push water out, or sometimes when filling the system you can find the leak. hope this is helpful.

Probably thermostat sticking or bad water pump. CK the belt to the water pump to see if it's loose. If the thermostat sticks, water can't be pumped thru the motor, overheats and overheats the radiator causing hot water or steam to build up pressure.and the relief valve will open allowing the peessure to be relieved and blows coolent everywhere. If the radiator overheats turn off motor wait until the radiator cools before removing cap. been there, done that-------once

yeah most likely a blown head gasket. if it blew across to a cylinder then compression will build pressure in the cooling jackets of the head and into the cooling system

The head gasket has gone so pressure builds up in the cooling system and forces water out of the overflow

You need someone to take the head off , skim it and fit a new gasket

it could be air lock , very common on those engines, more likley is a slight headgasket leak