I have flushed system , new thermostat, no leaks detected, only overheats when stopped in idling position, doesn't when traveling highway system. Water pump seems fine also.
What is the next step to figure this out on my own ?

Replace the radiator--it's likely phosphate scale contributed to its demise. Once you install a new radiator, or have the old one rodded, only add a 50/50 mixture of traditional green antifreeze and distilled water.

https://www.askmehelpdesk.com/cars-t...tml#post235973

On the fords they had a problem with the intakes leaking because they were made of plastic they have a new version made u can get made with alumium