Converter?

Hi, I would like to confirm with you guys before going to the mechanics

I've replaced my muffler a few months back and I do know that I have to replace the converter as well - (but hasnt yet) my car is a 1990 acura integra gs / auto

the other day, I'm having problem with my car going into gear

the car would start fine - but it wont grab any gear. I could move to R, D, N - but it's not 'grabbing' it. Also, it would make a grinding noise when I try to go to '(p) park'

is this because I need to replace the converter or something else as well?

Input would be appreciated - thanks guys