To start if your truck overheats in about the first 10 minutes after starting and you have a surging or bubbling noise then your thermostat is stuck and needs to be replaced. Also if your radiator coolant appears to be rusty your heater core may be plugged. So, while you are replacing the thermostat back flush the heater core also. Also check your radiator internally to see if it needs to be rodded and cored. It may have poor flow characteristics due to obstructions in the tubes from deposits and rust. This should fix all your cooling problems at once if you address all the above items.