Just thouht I would add. I hear the same thing after let off of throttle and when I turn off the ignition on my 08 F250 FX4. Didn't do this unitl recently. Only have 31,000 miles on the truck.
I have been battling Ford for the last year with problems with my 2008 F250 FX4 JOB #3. No matter what they are telling ya'll. A little smoke, i.e. a few seconds, is normal every once in a while. Heavy smoke is not!!! Should have had my a** kicked for buying the first new of all these new...