[01Motorsport]

2000 4.7's only have one cat, 2001's have 3. 2000 has one O2 sensor, 2001 has 4. Any good independent muffler shop should be able to install a Magnaflow y-pipe ($35 part) and Carsound/ Magnaflow hi-flow cat. ($130+ part). The factory y-pipe is a dog; only has 1 1/2" entrances at the "Y". Check out www.magnaflow.com under accessories. BTW, OEM pipe diameter is 2" from the manifolds. I went with 2 1/2" after the "pre-cats" on my '01, the Y, and a 3" exit to a 3" cat. Good for about 1 mpg improvement to boot.:banana2:
Also, '00's had 65mm throttle body, '01's and up 68mm...easy swap.