do you know what transfer case is in the 'rango? you can get a teralow kit (4:1 instead of 2.72 that i'd guess you have) for the np231, which is big with the jeep guys. if you have the 242 i don't know. i guess you could swap a 231 in, although i don't know any of the details for that.
the teralow kit will probably run 1200 or so last time i checked, and to install it you have to pull the transfer case out of the truck.
IMO i would just regear your axles and run 33s. cause 33s are much cooler!