Originally Posted by namretsud
Most newer vehicles are rev limited by the engine controller while not in drive. Another possibility is that you have a cat starting to go out on you. you can test by removing the o2 sensor on the side you suspect and tie it off somewhere safe while still plugged in and go for a drive. If you see improvement, then the cat on that side is going. Found this thru experience.
.........OR just use a IR Thermometer to test the input and output temps. The outlet should be 100* hotter than the inlet after running @ 2500 RPMs for 5 minutes. If not then you have a bad cat.
What namresud described is an incorrect way to test and will cause the vehicle to stay in Closed Loop operation (not good)