The 3.9L V8 is not in any way known for head gasket issues, and unless this vehicle was significantly overheated for a period of time (which the engine processor wouldn't allow, actually, since it would cut power to keep the overheating from getting worse), I would instead suspect you may be seeing a little oil burn off (your white may be more blueish - white...).
White smoke from tail pipes is a sure sign of blown head gaskets. You need to do a compression test, and a coolent pressure test to verify. Also look for signs of oil in the radiator, or coolent in the oil.
Normal exhaust contain a very high water content. This water vapor can condense in a cold exhaust system and cause steam to exit the tail pipe. This effect is most apparent in the winter when it really cold out side. That is why all cars during the winter months seem to have white smoke when running. After the exhaust system gets fully warmed up from the hot exhaust the smoke usually stops. During the warmer weather this effect is almost never observed. White smoke during warm weather means excess water is getting into the combustion chamber. This water normally comes from the cooling system either because an intake gasket is leaking allowing coolant to enter the intake runners and the get into the cylinders through the valves or it means that the gasket that seals the head to the block is leaking and coolant is entering the cylinders directly. If your radiator is low, then you know it is being burned in the cylinders along with the gas. If this condition is severe, the engine may also be mis-firing because water does not burn and it displaces the fuel causing the miss. Another side effect of leaking gaskets may be water in the oil. Pull the dip stick to see if the oil looks like a chocolate milk shake. These are serious conditions that can be car killers if left unattended.