96 having California Smog problems

I have a 96 4x4 with 120Kmiles that's had all recommended servicings at my local Toyota dealer. It's been troublefree, but now will not pass the new California Emissions (SMOG) Test. The dealer has replaced the catalytic converter and muffler and done two chemical treatments to remove engine carbon and still can't get it within tolerances. Has anyone heard about this problem in California with other 4-runners?

What part of the test can't it pass?