Sounds like the thermostat. I had the same problem on my dodge and this is what I did. I started and changed the thermostat. That didnt fix it so I did the water pump since it was the next cheapest thing and it fixed my problem. If neither of those work for you I would see if the hoses are vacuuming shut. Sometimes they can collapse in on themselves if they are going bad. If they are good then the radiator is your next bet. The nice thing is that there is only so much in the cooling system you have to look at. If it persists, it may be something more serious.