good advice Steiner! X2If you have the 2.73 you'll need the gears, carrier, and install kit. If you have the 3.23 you won't need the carrier.....but if you have the 3.23 you probably wouldn't be wanting to install 3.73's. Install alone will run around $500 typically and if you'll have to get the PCM reprogrammed to correct the speedometer, don't know if they make tuners for OBD-I cars. May be better to check craigslist and the local junk yards. The V6 auto models with performance pack were available with a 3.42 and limited slip, six speeds came with 3.42 limited slip so you can sometimes find those. Also if you have traction control you have to look for a four channel rear (has a sensor on each side instead of just one sensor). I got a four channel 3.23 complete rear to replace my 2.73 for $150.
BTW, ls1tech.com is a much better website for fourth gen info.