Rose,
We don’t have TiffImageLayer in 2.0, we can only open a tiff with imageLayer using GDI+. Do you mean that? Can you try GdiPlusRasterLayer in 3.0 to open that Tiff file with GDI+ too?
GeoTiffRasterLayer used a 3rd part assembly which supports GeoTiff (Geo Information included in that Tiff file) as well as many kinds of Tiff files (there are couple kinds of Tiffs although they have the same suffix). If you found some tiff files which have better performance with GDIPlusRasterLayer than GeoTiffRasterLayer, could you send them to us so we can have a further investigation here?
Thanks,
Ben