 The 2008 f350 6.4L turbo diesel dually 4wd is junk. Mine only has 69,809 miles on it and still has Fords extended manufacture warranty and i still had to pay for $10,000 in repairs for a whole new fuel system.  I get my oil changed, separator drained, and fuel filter changed as required, every 3 months, by Ford and its on record and its about $225 each time. Apparently even though Ford says this is a diesel truck, it hates diesel.  The fuel system automatically sucks up all the water and junk thats in diesel before it uses the gas. Therefore everything rusts.  Ford knows there is an issue and there are blogs all over about the high pressure fuel pump so check it out. Plus you get a whopping 5 to 6 mpg when towing anything.