Apologies, I mis-read data as date so my first comment is kind of irrelevant! (The regular Friday evening rush to leave work!)
As for your truncation problem, I'm presuming that you can actually see your data is being truncated? DI Studio will not truncate your data unless it is told to do so, and it won't even map you column if the target is shorter than the source, Meaning the problem is certainly in the external file.
I'd suggest you've got one of the following issues
Your LRECL is too short meaning just your last column has been truncated.
or
There is a difference of opinion between your Length, Informat and Begin/End positions (The length of these should all be the same). Don't trust the import wizard, it does get things wrong occaisionally.