Last year I moved into a home that is about 25 years old. It has a new Trane AC. The problem I am experiencing is that if I set my AC thermastat on 78 degrees my AC runs all day long without reaching 78 degrees. It reaches 79 degrees and just stays there or it reaches 78 degrees but keeps running. During the hottest part of the day the temperature inside the house reaches as much as 81 degrees when set at 78 degrees. I don't know if I am dealing with an air conditioner problem, a thermastat problem, or an insulation problem. Late in the evening when the out side temperature drops the AC will eventually reach 78 degrees and shut down for a short period of time. Any suggestions on what I am dealing with? I have already put in new windows with current thermal protection and ratings.