intermittent missing

[cmsmoe]

I have a 99 F550 7.3 and recently it started blowing white smoke and missing. I shut it off and drained the water sperator. After that it runs fine for 35 to 50 miles than the same thing happens. I shut the truck down when I drain it and have had the tank checked for water. I'm wondering if something is resetting when I shut the engine off. Hope someone has an idea.