what can be making my Legacy keep overheating?

I have a 2012 Legacy, I replaced brand new radiator, water pump, thermostat, temp sensor, timing belt, hose clamps, refilled the car with gallons of coolant and it keeps overheating, the mechanic said it wasn't a head gasket (as he would've done it) but its not as no other symptoms besides loss of heat/oerheating engine. i am so stuck because bought the car used without being told of any issues, spent over a grand on repairs and im still stuck at square 1 and i have a job to get to so idk if i should just sell it for what it is and take a massive loss or keep investing thousands into a older car?