If memory serves me correctly Pacific Digital drives are just 'rebadged' NEC or LiteOn drives, which just happen to be two of the best drives on the market right now.
Lets start with what burner you really have. Download
DVDInfoPro and let us know all the what info it says under drive information as seen in the right hand side of
this screenshot.
Next let's get the
media codes from the media you are using so we know what you are really dealing with (if you don't feel like downloading
DVD Identifier you can use DVDInfoPro to get media codes as well).
Get back to us with that information.