@Syleng1 gives good advice. If water is flowing through the heater, core properly, which it sounds like it is since both heater hoses are getting hot, that will remove the heater core as a suspect. Then it comes down to some of the other suggestions, as for cables, or possibly a vacuum operated vent, that is not opening to allow air to flow across the heater core. I had a Dodge Caravan once that had poor heat. I back flushed the heater core with a garden hose, and then it worked OK after that. Have you used an IR thermometer at the thermostat housing to test the water temperature inside the engine?
