Non-mopar tech question, sorry...

Here is my two cents worth. I think it boils down to two things.
1) Is the engine heating up? If you do not have a temp gauge that you are 100% sure of, but a laser thermometer. They sell them for as little as $40 and they are VERY handy. You will wind up using it a lot. That way you can accurately determine if the engine is warming up. The easiest way is to check the temp at the thermostat.
2) Next, (assuming the engine is warming up properly) you need to determine where the hot water break in continuity is. For example, if everything up to the firewall is 180 degrees and the heater hose coming out of the firewall is 80 degrees, the heater core is plugged (assuming it isn't leaking). That is when backflushing it (Forcing water through it backwards of the normal flow) will work well. I did that in a Dodge Caravan once, and you should have seen the crap that came out. The heater worked much better after that.