1) were all files created exactly the same size and time?
2) were all files created large enough for all data and data growth or did you let autogrowth manage the size as you loaded data and began processing?
3) are all files now exactly the same size?
4) are all files part of the same filegroup?
Best,
Kevin G. Boles
SQL Server Consultant
SQL MVP 2007-2012
TheSQLGuru on googles mail service