Please help my 2001 gs300 has been running sluggish for week and especially when I floor gas pedal, and today on the freeway it would not go past 60 MPH,Then suddenly it decreased to 50,40,30 MPH then I was going 10 MPH on freeway and I had to pull over,after another mile to car stopped.I had to get it towed,The car runs now but barely to about 20 MPH and the check engine light has been on for a year but I was told not to worry its just the O2 sensors,I had it ran for codes 2 days prior to this that happened today with the car shutting down and the code was PO 420,I don't know if I need a new 02 sensor or a cat converter,please help,Thank you your time is appreciated.

 

The cat sounds like it's clogged. I'd replace it and it should be fine.

 

o2 sensors should be a worry - they are a critical component for the engine control unit...