All exhaust has some moisture content. When the exhaust system is cold the hot, moisture laden exhaust travels through the exhaust system and condenses some of the water vapor. This condensation can be seen. If it is really cold outside, the exhaust system never really warms up. That is why, in the winter, virtually all vehicle have white smoke coming from the tail pipe. If you have coolant leaking into the combustion chamber, the moisture content of the exhaust will be higher than normal. You may be able to see this water vapor when you first start the truck. Have someone perform a chemical block check. The test is performed by sampling the gases present in the cooling system. The block check fluid changes colors when exposed to the carbon dioxide that is present in exhaust. If the color change occurs, then you have a combustion chamber leak.