I picked up a FM40 series 2.5" cat back from Rusty's off road for my 98, and loved the sound and ease of install.. I also picked up a direct replacement cat from Auto Zone, and it was a quick install and would have been even easier if I had done it at the time of the exhaust install.. Keep your eyes open at local PNP's and local Jeep forums for a 99+ IM, I ended up picking one up for pretty cheap with a spare TB off of my local Jeep club forum..