If it's under warranty, then there's no loss in getting the DPFE changed.
However, if this doesn't solve the problem, then I'd check the EGR passages. They are located *behind* the TB gasket, and are located on the intake manifold (not on the TB itself). You need to removed the TB and gasket to even see them - they are three channels etched into the intake manifold. When they get clogged, it's sometimes hard to even tell that there are passages there! Once you remove the TB, you'll need a new gasket (~$2.00). If they're plugged, clean them out, install a new gasket, and make sure you disconnect the battery to clear the code. You should then be all set.
Good luck!
- Mike
