1997 Running Board problem

I recently purchased a set of OEM running boards that came off a 1999 Tahoe (old body style) to put on my 1997 Tahoe.  The brackets that are on the runningboards dont match up to the frame rail; it seems that the brackets don't extend far enough back to bolt onto the frame.  Any idea what I am missing?  The dealer said that they sell the same running boards and brackets for all 1995-1997 Tahoes... why don't these fit?

Did you have running boards on the truck originally?  If not, the mounting points on the truck are missing completely on your truck