we replaced radiator, hoses, thermostat its still overheating What did we miss?

its starts to heat up when going to work which is only 6 miles away. Idling, especially on hills and traffic the gauge goes higher. It did not boil over at any time. It seems the highway speeds no problem. We keep on moving and not stopping, it will take longer to heat up. It only started recently.

Have radiator cooling fan 'CLUTCH' tested .. Hopefully the HD (3 row) radiator was installed..(?) .. Good idea to have temperature gauge accuracy checked.