Overheating and engine shutting off at low speed

Hi, I am not to sure how many miles I have exactly but it's around 230,000 miles. I am having some what of the same problem it starts and some day's I drive it and it does not do it but other days it does. It stalls out at a light or stop sign or like on the highway it stalled out in traffic. So I put it neutral so I could start it again and started driving it again but when I would slow down to thirty mph or lower I would put it in neutral so it does not stall out on me. I have just recently had a tune done my fuel pump, fuel filter replaced and the idling gauge. My radiator has some leaks on the top so it gets warm really fast and it smokes like it is overheating but the gauge does not go past the middle line on the gauge. I keep telling my friend we need to change the radiator. Do you think the radiator is the problem or what could it be? My cousin also mentioned that I might need a new thermostat. I do not know what I need to do.