Q: Car overheating, all but head gasket replaced/cleaned/flushed. Res overflows and bubbles, no coolant in oil/ext smoke. whats left?

My car is overheating. I replaced the radiator, thermostat, water pump, fans, fan switch, engine temp presser sensor and reservoir. I have flushed/cleaned/removed air multiple times from the system and replaced with new coolant.

As the car heats up (about 10 min drive time) the coolant in the reservoir slowly rises to the top (20 min driving) and has a ton of bubbles in it. Once the reservoir gets to about 90% full, the car uncontrollably overheats. Fans come on but stop after about 2 minutes (almost like it gave up trying to cool it down). While the fans are on, the temp is stable, then rises after about 30 seconds. Once they turn off, the car overheats as much as possible. I am also losing a lot of coolant, a lot more than is leaving the reservoir.

There is no coolant in the oil, residue under the radiator cap or white smoke from the exhaust. Is it a head gasket issue? Or what else could cause these symptoms?

My car has 166000 miles.
My car has an automatic transmission.