Hello and welcome to Just answer.com, Super mechanic here. About your vehicle.
There may be a sticking thermostat but you will want to make sure that the radiator is not clogged up. When the engine is warm, (or hot) you can check the radiator for any cool spots with either a digital temp gun of sometimes your hands. Be careful not to get burned theough.
If there are any cool spots in the radiator that means it is clogged in those spots. You might want to first try a new thermostat and flushing the cooling system out and see how it does.