loss of performance

i do not drive in the upper revs much, so i really do not know when this started. but i am experiancing a loss of power, above 3000 rpm @ W.O.T. . so far, i have replaced the fuel pump (with an A C DELCO pump), fuel filter, air filter, cleaned the mass air flow sensor, the dist. cap, rotor, wires and plugs are only 1 1/2 years (23-25,000 miles) on them. it does not seem to break up like an ignition problem would. it just gets weaker and weaker to the point it quits gaining revs about 4100 rpm. i am beginning to think it may be the catalytic converter is plugged up. but i have no idea how to check that. would an bad o2 sensor cause this, without triggering a check engine light?

Remove the oxygen sensor in front of the cat conv. And try driving it , if it runs better it is your cat conv clogged. Which I guarentee it is. Remove it , spray the bolts first with PB blaster , so you don't break the studs. and dump it out. Then get a new one. Also ask yourself how old is the cat conv ? How old is the fuel pump ? And how old are the poppet valves ?

the fuel pump was replaced about 6 months ago. that and a new fuel filter. as far as poppet valves, i have heard the valves in the cylinder head refereed to as poppet valves, but only by British enthusiasts. i have no clue what you are referring to. my question about driving the vehicle with an o2 sensor removed, is what is that going to do to the fuel injection mixture? as long as the hot gasses are not pointed at something that is going to melt, or catch on fire, i do not have a problem doing that. but if it is going to artificially going to make the mixture richer, it may run much better simply because of that. i am not getting a check engine light, i do not know if that means anything or not. the weird thing is it runs great below 3500 rpm. the one thing i have noticed about this, is when driving it, and this has been this way since i got it. is that as i am accelerating, it feels like the timing or fuel enriching is graduating in steps, rather than a nice smooth flow.