Mine does it very predictably especially on cool days <60F ambient. If I come to a stop at a long light while in regen and the exhaust cools down, I'll belch white smoke for the next minute or so. Letting up on the throttle makes no difference.

Dealer says this perfectly normal. There's a TSB for the CAC for white smoke on humid/rainy days but that's a different problem. My smoke is definitely not steam just from the way it dissipates.

A buddy of mine had the same truck as mine, and he was complaining about the same. He videoed himself blowing a smoke screen down the freeway and showed it to his dealer. They said it was perfectly normal too. I posted his video somewhere on one of these forums a while ago. Can't remember where I put it.

My guess is the CAT cooled down so much to be ineffective at burning the regen fuel. Instead, it fizzles like squirting lighter fluid on hot coals.