I have a 97 cadillac with a northstar engine I keep having over heating problems with it. It gets worse if you have to set in traffic or pulling a hill going slow behind someone. Does anyone know what could possible be wrong with it.

That sounds like the radiator fan is not properly functioning. My second guess would be a water pump. How many miles do you have on it?

Do you have the A/C on when it does this? If not try turning it on, if that works it is the fan. If the A/C is on or if you prefer, pull over to the side of the road, turn the A/C off and then see if a radiator fan is running.