My 2004 buick lesabre blowing cold air not hot , but I notice when im on the freeway its trying get warm

This can occur if there is a blockage in the heater rad, or the blend door actuator that regulates air temperature into the cabin is malfunctioning, or the cooling system thermostat is malfunctioning. You can check by carefully feeling both heater hoses under the hood after the car has been run for a while - if one is hot and the other is cold, it's a blockage. If both are cold, check the thermostat. If both are relatively hot, it's usually the actuator.