The impossible to solve overheating problem

Unplug the fan. Disconnect the upper hose at the radiator. Prop the open end higher than the rest of the system. Take the radiator cap off. Start the car. Let it warm up to thermostat opening. Run garden hose into radiator at a reasonabe flow so as not to make a huge mess. Water pump should flow water out the top hose at a rate in relation to engine temp. As it warms up more should pump out. All sorts of things can be observed. If cold water can't get through fast enough, radiator may be plugged. If engine remains at a proper temp through different rpms maybe radiator isn't cooling well enough. I would triple check the thermostat.