heater not maintaining speed

Hello, do you have a fan speed switch that is manual, or do you have temperature based settings that create an "automatic" temperature control? If automatic, suspect that the sensors in the vehicle measuring temperature may not be providing proper data to control the temperature desired. Or, you could have another climate control system issue influencing operation. If manual, the switch or wiring or motor itself could be of concern. A shop near you could help -- here's a way to find one: www.repairpal.com/repair-shops