The Nissan Path

I have a question and I have noticed you have a far amount of knowledge with these vehicles so any help would be greatly appreciated.
I have a 95 pathfinder 5 speed 3.0 ..... the problem - when I put any tough load on the truck if feels like it is studdering .... mostly happens in 3rd 4th and 5th if you try to accelerate to fast. If you drive really easly it doesnt do it. I have replaced plugs , wires , distrubator , rotar , fuel filter , ran seafoam through it. I'm wondering if my catalyst convertor could be clogged up or maybe an O2 sensor. Any ideas all help is greatly appreciated!!!

It could be an O2 sensor; if it's more than a few years old and has over 100,000 miles on it, it wouldn't hurt to replace it...or you could test it if you have the equipment to do so. An exhaust system backpressure tester can tell if the converter and/or exhaust is restricted. A failing coil could do the same thing. Any chance the problem is a slipping clutch under load?