When I started up my truck yesterday, it was puffing white smoke at idle for a few minutes, then everytime I let off the throttle for about 5 more mins. It seems to happen when its humid out and the truck's been sitting overnight. Doesn't seem to be oil, coolant, or anything else dripping in/on the engine. Is this common?

 

You may need your ECM reflash as there is a TSB out for the white smoke at start up and if it still does so after a reflash then you may have an injector problems.

 

Does the smoke smell like diesel fuel?