1999 Chevy Camaro hesitation on acceleration during gear ch

I recently bought a 1999 z28 camaro and in between changing gears especially in between 1st and 2nd and in between 3rd and 4th it surges. I was told maybe the catalytic converters were clogging. I replaced the factory muffler I was also told the factory muffler could be my problem with it been nearl 10 years old but it did'nt help nor hurt it did give a better sound so I didn't consider it a loss. What is your opinion on this. Everybody I've talked to seem to lean toward it being somewhere in my exhaust sayiny the catalytic converters aren't letting it breath correctly whenever it pulling away during acceleration through the gears or when its pulling.