New thermostat in the last month and the furnace keeps up the same problem, air conditioner works fine, have to set thermostat around 75-80 to keep house around 70.

Check the anticipator setting. It sounds like it is set too high (heat). If it's electronic ignore this. Also, you need to check the location because that affects it greatly. It must be 3 feet from an exterior wall and from any false heat source. A cold draft will make it come on too much and a heat source like a lamp will make it act like it is now. I bet you did not need a new t-stat. DrTom4444