I recently had the heater core replaced in my Envoy. The heat gets hot but does not come out very fast. I was thinking it was the blower motor but if I turn the air condition on the air is cold and blows out really fast, but as soon as I turn the temperature up to 90 degrees to turn the heat on the air diminishes. It sounds like its blowing out fast but its not. With this also the vent in the rear passenger console only blows out warm air and will not get hot. Any ideas what could be causing these problems?