If you have a code in your computer saying you have low catalyst and your car seems to be bogging down then i would go that route first. Replace your converter, and your O2 sensors again.
For a 1998 car, this seems kind of strange that your cat's are clogged up already, but anything is possible I suppose.
Also, check your transmission fluid, if it's not blood red or smells like garbage/burnt, you should change it. It will improve the way your car shifts and the clutches will grab eachother better.
Secondly, don't even bother using that injector cleaner that you pour into your gas tank. It's a placebo, and rarely has any real effect. If you want to get your injectors cleaned, go to a shop and get them to hook your car up to a MotorVac machine or something. Then after that, make sure you get name brand gas like mobil, shell, sunoco. Not all gas is created equal, and the cheap/no name gas stations don't have quality fuel.
On any car it is hard to diagnose this kind of problem from a distance, since there are so many possible causes. I hope I gave you an idea of where to start from.
Good luck!
Ben
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