2003 Nissan Sentra Q&A

2003 Nissan Sentra Question: My cat was replaced and my car is still chugging why?

plugs replaced coils......please help -
Answer 1
Check engine light on? -
Comment 1
code was cat needed to be replaced....but got in car drove away from repair shop and still didn't sound right. More I drove back to the chugging sound like it was missing a cylinder as before......and yes light came back on not right away but within 2 days.....please help -
Answer 2
BECAUSE THAT WAS NOT THE PROBLEM.HAVE CODES SCANNED AND POST -