1999 Volkswagen Jetta Catalytic Converter

Engine Performance problem
1999 Volkswagen Jetta Automatic 75000 miles

There are 2 codes showing up for my car - one is a bad catalytic converter and the other is "misfire" which I've been told implies basically a tune-up. I have been having issues with my car recently where it seems to hesitate when I accelerate but then will suddenly rush forward, and I've also noticed less power going up hills. I know these are both symptoms of a bad catalytic converter. My question is: if I get the tune-up, will this help with the other matters, and mean that I could possibly not have to replace the cat. Converter right away? Or would there already be too much damage, and it needs to be replaced?

Also: I had my car checked a few months back, and was told that there was a problem with the O2 sensor, but this code didn't come up this time. I have also read that a problem with the O2 sensor can cause the computer to misread as a cat. Converter issue.