Red, need more info. Do you have a good shroud on the radiator? If so, is the fan inside this shroud and close to the radiator so it pulls a good amount of air across the core? I would guess from your statements you have a mechanical fan.....how many blades, and do you have a clutch on it?

As we have discussed in the past, heating up at lights is generally caused by insufficient airflow. Going down the road forces air across the radiator, but at lights you are depending on your mechanical or electric fan to do that for you. Even if you go to an electric fan you still need a good shroud otherwise the fan only pulls air across the section where the fan spins. With a shroud it pulls across the whole face of the radiator.

Lots of other factors, like timing (do you have vacuum advance on your distributor ?) Type and opening range of thermostat, etc.

Don