lack of power, cant go past 3000rpm

My Trailblazer has no power and will not go over 3000 rpm. I have replaced the spark plug, coils, vvt and cam shaft position sensor, disconnect O2 sensors, cleaned throttle body, still rough idle and wont go past 3000 rpms. please help

When that was MY Trailblazer, the catalyst was plugged. But that's only one possible problem of a dozen that could cause this issue.

Connect a scan tool, look at the data stream. Test the fuel pressure at idle, and under load at 3K RPM. But while you're in there, unscrew the O2 sensor ahead of the catalyst, leave the hole open, fire up the engine and see if things improve.