1994 GMC Jimmy 4.3 liter V6 engine OVERHEATING!

Recently had the water pump changed because it was leaking and shortly after the engine started overheating! It overheats after being driven for a mile or so and will cool down at red lights or if I idle at a stop sign for a few minutes. It gets very hot and stays hot when driven on the interstate (only tried that once). I haven’t been using my AC because I thought it would make things worse but I turned it on yesterday while driving and the car ran perfect no overheating at all! I’m at a loss and need some advice!