did you try:
convert image.tif ptif:newimage.tif
do you get a line for PTIF when you do
identify -list format
that looks as follows:
PTIF* TIFF rw+ Pyramid encoded TIFF
are you using the latest version of libtif? is there anything that needs to be configured in the libtif install for pyramid encoding?
see also
http://www.imagemagick.org/Usage/formats/#tiff
and
viewtopic.php?f=3&t=12723&hilit=tiff+pyramid
and
http://iipimage.sourceforge.net/documentation/images/