How do I know if the heater core is clogged or the actuators need replacing?

Thanks. So if the hoses at the fire wall are the same temp there is good flow through the core and the actuators are causing the problem? Can bad actuators cause the car to overheat?

No; The temp/blend actuator just moves a door from heater core to evaporator. If your getting hot let me know the symptoms as to when does it get hot.

Thanks, that's what I thought. OK so went out and started it, ran it for about 30 minutes. Temp sat at 200 then started to go up, heard the radiator fans kick on around 220 and the temp held steady, then went up to about 245ish. Turned on the cabin fan and cold air only, turned it off. The temp started drop back to 200, then 180, then all the way down to 165 before climbing up again resting around 200. Turned the car off to check the hoses. Hose from the radiator to the therm was very hot, one of the hoses into the firewall was warm/hot the other was cold. The return hose to the radiator was kind of warm, not cold or hot...a little worried about the flux in temp as I know this could be a symptom of the gasket failing, however, the mechanic said there were no leaks four days ago and the pressure was good. It did overheat today though, I pulled over and turned the car off within a couple hundred feet. Thoughts? Thanks for your time I greatly appreciate it.

OK the first thing is the heater core is not allowing coolant to circulate, before changing the core, try to flush it again, and try an inline coolant filter to see if you can catch the debris in the cooling system before it gets into the heater core. Now the temp raising, if sitting idling, it will get higher then running down the road in normal conditions. The fans will come on at a higher temperature, but it should cool as you stated it did. Now driving and it overheating is another issue. It should not overheat driving down the road unless your in stop and go driving, but the fans should help keep the temp at normal range. If it overheats and doesn't cool down while driving, you could have an issue with the radiator.