Stuck at 3500 RPM @ 60-70 mph

I have an 3.8L '02 Camaro with 82k miles. The car was driving normal until I went to pass at approx. 70 mph, and it lost its power. The car drives normal at low speeds, but it will not achieve over 3500 RPM when accelerating at high speeds or going up steep hills. It does make some noise when trying hard to push it over. Check engine light diagnostics revealed a forward oxygen sensor. I replaced the sensor, and reset the light. This did not fix the problem. While revving at idle the engine sounds strong, and there are no exhaust odors. So it doesn't sound like a catalytic converter or exhaust problem. Does it sound like a bad Manifold Air Pressure (MAP) or Mass Air Flow (MAF) sensor even though diagnostics don't indicate it? If so which one? Any suggestions are appreciated. :)