When i flushed the system I pull the heater core hose to check the flow with the engine on at idle. To me it didn't look like it was enough flow, but i don't know what the flow should be. 1gallon a minute? 10gallons a minute?

If i had to guess, I'd say at idle it was maybe 1/2 gallon a minute or less.

 

Ok, did you replace any of the hoses?

 

IF the heater core is under served with hot coolant, their will be a large difference between entering and leaving temps. If the in/out temps are close to the same, you are not giving up heat to the air flow. Air is bypassing the coil or the coil is scaled (insulated) and not transferrring heat.

My question to everyone - what is the difference between a $35 and a $55 heater core. Thinner copper or brand name?

 

Yes, the enging should be runing at 195 and will get up to about 215 on hot days or carring heavy loads. it sounds like the thermostat is staying open and not allowing the enging to heat up properly
i would start with that one first, its a low cost repair.

 

yes if the heater core was flushed but all the debree was not removed the heater core will pass coolent through and not allow heat transfer to the passing air over the coils. the temp will be close to the same on the input and out put. but the first check would be is the enging getting up to running temp to supply the core with the hot coolent it needs. then start with the flow check and temp checks.