catalytic converter or o2 sensor? on 2003 Hyundai Sonata

I just had engine rebuilt, now pick up is sluggish. Mechanic says needs catalytic converter. Does that sound right? What are symptoms of bad converter?

1 answer
BAD CATS WILL CAUSE LACK OF PWR ISSUE ALMOST LIKE RUNNING OUT OF GAS ON EXCEL. YOUR CAN CK THE VAC. IN YOUR ENG TO DETERMINE THIS. A GOOD RUNNING CAR SHOULD HAVE APPROX 20 INCHES OF VAC,INSTALL A VAC GAUGE AND EXCEL TO ABOUT 1500 RPM VAC WILL DROP AT 1ST THEN RECOVER IF IT STAYS LOW POSS PLUGGED CATT. VERY COMMON