96 4.6 cobra overheating issue

So I have a major question and looking to get an answer to. I have worked on my brother's 96 4.6 cobra by taking care of over heating issue. Have changed radiator from stock to mishimoto radiator, water pump, thermostat(180F) and temp sensors. Still over heating. Secondly heater core stopped working so we think it may be clogged and not busted since there's no leaks inside vehicle. But overall even after doing a bypass to see if engine would still over heat with out heater core it sure did. Only thing I can think of is a head problem or internal problem where water flow is not properly circulating. Water goes back or comes back to reservoir and shoots it out. Last of few test to do is running water through heater core and hope it comes out and also doing a leak compression test and see if we get an answer if it is a blown head gasket.

Thanks in advance if someone can help with an answer.

Yeah so the weird thing is I had bled it completely when I changed radiator and thermostat but when I did temp sensors in it because I lost coolant replacing them I bled it again and that’s when the heater core stopped working. My only resort that I could think but not 100% sure is it may have a blown head gasket that is causing all this mess.

Yea that’s exactly what I was gonna do with heater core this weekend but found out today that the car was getting picked up and taken somewhere to get taken care of so hope it gets fixed.

1st time
First we got radiator flushed and cleaned out and replaced thermostat. Took it to get all air bubbles out and ran good until now

2nd time it overheated.
Everything I’m explaining got changed out.

Yeah it was overheating and started with radiator. Ran fine after changing. Then thermostat after like 3yrs had to change again. Ran fine after that. Water pump only got changed because I pulled out to check if any bearings were maybe messed up since it had been since like late 2016 that it was replaced and well had taken radiator off to double check that wasn’t clogged. Hope I make sense how I’m explaining all this. lol.

But honestly all this started like a week or two after the clutch got replaced. So that really is what throws me off.

Again hope I make sense and haven’t lost you lol