catalytic converter for a 1998 mazda 626

I have a 1998 mazda 626 with 87000 miles on it i had it at the garage because my check engine light was on they put it on the computer and told me the code was for the catalytic converter how do you know when that needs to be replaced i am having some hesitation when putting my foot on the gas it kinda feels like the transmission is sliping everyone is telling me that those are the signs that the catalytic converter needs to be replaced can you just tell me what you think....thank you
Gabrielle