Airconditioning not reaching temperature of thermostat

I have a goodman a/c with electric heat strip (10kw) and vey recently it stated to turn off before reaching the set temperature. After a few minutes it will restart and run for a couple of minutes and then shut down again without reaching the setpoint. It always stops at 66 on the white rogers...

I have a NOMA thermostat (model 52-2558-8). After reaching the programmed temperature, the furnace stays on without shutting down (8 degrees before I manually shut it off). Is this a thermostat issue or a furnace problem?

Similar problem Chickendoc has. The pemperature lebel shown in the thermostat is 67 while the setting is 72 when it stops. The furnace run short period of times. Some times it re-starts a few times stopping/re-starting succesively at same period of times. Finally, it gives up. What we are doing is...

Installed new White-Rodgers board in lennox furnace. Furnace runs but shuts down before reaching thermostat temperature.