==Not Introduced in 1998!== 
 I'm sitting right here with my 1992 factory service manual. It makes repeated reference to the F-Super-Duty, which is a modified F250. In addition, I have a super duty axle installed on my 1992. The model has been around since before 1998! It was formerly a model of F-250, but the 2011 is ALSO called an F-250. To leave out the earlier super duties is a total failure.