Hello DJ,
On some models there's one or two air bleed ports, once the system has been drained and refilled there can be pockets of air trapped in system.
If it has any of these--as the system is heating up, open them slightly to see if any air escapes.
Also, check to see if the radiator cap pressure is correct for your vehicle; the proper pressure is important.
You can feel heater hoses to see if there is a difference between them, if in-going hose is hot and out-going is cold or somewhat cooler, there could be a restriction in heater core. Check the top and bottom radiator hoses if you have flow, it should be cooled by the time water gets to lower hose, if it's hot--you might not have flow.
Some older model cars I've worked on in the past had a header bypass valve in heater hose in engine compartment which were controlled by the engine vacuum.
If you do not know the history on this car--someone could have put a type of radiator sealer in it.Not good!
Hope this helps
In Chist,
Walt, October 2008