1987 Nissan Pathfinder-Catalytic Converter question

I have a 1987 Nissan Pathfinder. It has the 6 cyclinder engine, is 4X4. My problem is this. While driving, its almost like its flooding or something. Ill be going, then itll stop accelerating. If I pump on the gas pedal sometimes it helps, but it will do it again 30 seconds later. I have already replaced my fuel filter, distributor cap, rotor, plugs, wires, and the distrubotr itself(i dunno my own strength). The way I describe my problem, is its like when you are using a gas powered weed eater, and you leave it in full choke and give it gas. How it speeds up, but has no power and bogs down a bit. My question is, could it be my catalytic converter. I bought the vehicle in New Hampshire, and it does have a good bit of rust dmg underneat. It has already burned through my floorboard under the driver feet area. I replaced my exhaust, it needed it, hoping that would help, but it didnt for long. If it could be the converter, how hard would it be to change myself? Im far from being a mechanic, but I do routine maint. Myself-the above stuff, oil changes, brake pad changes, etc. Any information would be really appreciated.