It is common to see the variable vanes inside the turbo seize or bind from carbon buildup. This causes an overboost or underboost condition when driving.
Car Problem Reports
Ford F-350 Super Duty Variable Vanes Inside Turbo Seize Due to Carbon Buildup
Ford F-350 Super Duty Problem
Engine Affected: 6.0L V8 Diesel Turbo
Average Mileage: 66,000 mi (52,000 mi - 80,000 mi)
Visitor, 2006 Ford F-350 Super Duty, 6.0L V8 Diesel Turbo, 52,000 mi
Truck sits for weeks at a time before being used. Sometimes the turbo doesn't work at all for miles then kicks in. Other times I get an overboost condition that sets off an overboost code.
Must be carbon buildup in the turbo vanes and/or EGR valve according to what I've read. Wish someone would post how much trouble it is to take care of yourself.