@User: "rthresh" is something else called "lumped resistance" used by digital switch simulators but not understood by SPICE simulators and not what you want. The sequence of commands you want to use to get full R-C extraction is:

extract do local
extract all
ext2sim labels on
ext2sim
extresist tolerance 10
extresist
ext2spice lvs
ext2spice cthresh 0.01
ext2spice extresist on
ext2spice

There are, unfortunately, a number of issues related to "extresist" that I have been attempting to work through. Currently it fails for capacitors, bipolars, and diodes. And its behavior with respect to hiearchy is not well defined, which means that your best option is to flatten the entire circuit before doing an R-C extraction.