What temp thermostat you using? A 160 or 180 may not cut it in Montana. Maybe switch to a 195 over winter. Another trick I have used in a vehicle where the heater just could not quite do the job is to cover the radiator with cardboard. You will notice that semi trucks cover their radiators during winter . You do have to be very observant when you are driving during a warm snap so as to not overheat the engine.
