Cooling issue, but this time it's to cold...

I'm not explaining this right. The heater works perfect, no problems. The heat coming out of the vents reflects the temperature of the engine, so if the engine runs cool the heat coming out is cool, not useful for warming humans. If the engine gains some heat at a stoplight the heat coming from the vents reflects this rise in temp. Then I start moving with the green light and the temp gauges reflects that the engine is cooling off and the temp of the air coming out of the vents also coincides with this, meaning that the heat coming out of the vents is not real useful anymore. This only happens when moving, sitting in the driveway it has no problem getting to 190, until I start driving.