Car overheating after several new parts.

Does your vehicle have a overflow tank that you can add antifreeze to ? If so bleed air from system like this. Remove cap from overflow tank add antifreeze to full mark leave cap off and start vehicle and let idle you will notice level in tank start to rise this is normal once thermostat starts to open level in tank will drop add more antifreeze to full mark then put cap back on. That should do it all air out of system.

Purge air out of the system.

If what you say is true you probably have a head gasket internal breach and simply cannot purge the "air" out of the cooling system, as EXHAUST gases are "percolating" into it continuously. Sometimes the system's heat-sinking ability is strong enough so that initially the motor will idle successfully; but eventually the leak becomes so large that the coolant will superheat and boil out even at idle. Note that this percolation pressurizes the system, so that if opened hot you could REALLY suffer a hor coolant explosion up into your face. BE CAREFUL! Note carefully that perhaps you're overheating simply because of insufficient cooling because of a blockage in the system. Most famous culprit is use of a small-bore aftermarket thermostat that reduces coolant flow on demand. So start by ensuring that you're using an OE wide-bore t-stat; you can grab a new one from a dealer temporarily to compare yours. Then check the rear heater hoses for partial blockage; back-flush them to clear, Check your radiator's EXTERIOR front surface for leaves and detritus. If it's aluminum it's probably ok. If an old copper one it may be shot. They're cheap anyway. OE water pumps are REALLY durable and reliable, so I wouldn't suspect that. The possibility of one simply not spinning is really low. As HGs are only two years old I wouldn't suspect them, but any cheap HG job that didn't include head-testing, new head bolts, proper torquing, could cause the new HGs to fail. A lot of Subaru mechanics working under warranty will simply slap on new HGs and bolts, ignoring the delay required in sending the heads to a machine shop to pressure-test for miniscule cracks and assure flat surfaces. As well, if the heads are shaved too much they won't sink enough heat, starting the pressure-cooker process all over again. It's hard to know.... A good test is to elevate the front of the car a bit, put a funnel on the radiator, fill halfway with coolant, and then start, adding coolant if necessary to stabilize the level in the funnel (put the AC on to keep it more stable). Then use a HC probe to read gases in the bubbles. If they're full of hydrocarbons instead of just air then you know you have an internal severe head gasket leak between a cylinder and a coolant passage in the head. Only solution is a $1.5k+ HG job...again! Time to move on.... (Disclaimer_ I service and sell 2016+ OBs/Legs in the Boston area.). Good luck.

Thanks for everyone's input. After trying everything with no success, I have determined it is a cracked head. There is also a slight bottom end knock which will more than likely get worse. I am going to look for a good motor to put in it. A fairly easy job. We can find them around here for around $200. Again, thanks for all the help.