How to fix overheating

I have replaced the thermostat, waterpump,
radiator, temp sensor, coolant reservoir, and all the
hoses. The fan does work and the car does not
blow any smoke out the the exhaust but it is still
overheating. I flushed the heater core and a lot of
stuff came out(looks like dried up stop leak), it ran
fine then overheated again so we flushed many
times and flushed the whole system. Car still
overheats so we are ordering new fan relays. Did a
combustion leak test and had no leaks. Does
anyone
have the same problem or know what else to
check? I know there’s a very small coolant leak
somewhere.