Ive read on other sites that the cat is blocked on it. and the cracked the bolts between the cat and the pipe and it worked. also was told to get the cat with four ports not the OEM one it will clock up to. also with that being replaced you need to get new O2.
Same people posted after that they ended up with same problem 2 months later (the O2 was making to rich and burned up the new CAT......