Heatpump that runs constantly in heat and cold

[rd0522]

If it is below 38 and I set the thermostat at 68 the unit never shuts off but if I set it to 69 , once it reaches 69 I then set it back to 68 and it will shut off - so the unit is capable of achieving the temp it is set at. The same thing happens with the AC. The first summer I had the unit I believe it did shut off but in the winter when it wasn't shutting off I called a new contractor because the installing contractor had gone out of business. They replaced the thermostat, they did do some wiring changes and slowed down the fan because it was blowing cold air plus it had been set for a 4 ton unit when it is is 3.5 ton. This change helped reduce the the blast of air that would hit you in face.
Could I still have a wiring problem?