Ford 7.3L Power Stroke (1999-2003) :: 2001 - White Exhaust Smoke When Letting Off Throttle

2001 SD F-250 SuperCrew 4WD, 7.3L (completely stock), 114K miles, automatic

We took Dad's SD for a 600-mile trip yesterday and today. The oil had 2000 miles on it, and we checked it before we left. The oil level was half-way down the hatch-mark, so we had added a little over a quart of oil to top it off, and I think that we may have added a little too much. Last night, when we got to the hotel and got out of the truck while it idled, a lot of white smoke that smelled like burning oil (like when you spill oil on an exhaust manifold) was fogging out of the exhaust.

It did this for a minute or two, then cleared up. All day today, on the way home (300 miles), about every time that I let off of the throttle either going down the interstate or stopping at a red light or stop sign, white smoke would pour out of the exhaust briefly, then stop when accelerating or in the throttle going down the road. What is causing this? Would too much oil (a little over a quart too full) make it smoke like this? The truck runs strong, starts and idles good, and no 'check engine' lights came on the dash.