Welcome to Justanswer, My name is Danny I am here to help.
I am very positive its the catalytic convertor but this will make sure your not missing something simple.Check for engine misfire. Check fuel pressure regulator for a leak. Check for coolant consumption. Replace the catalytic converter.
Let me know if you have any questions. If this was helpful please take a moment to kindly press the green ACCEPT button in the lower right hand corner. Thanks in advance Danny