0420 bad cat convert on 2001 Toyota MR2 Spyder

history bought car about 1.5 yrs..replaced all 3O2sensors..replaced ect sensor..bleed system...replaced bank 1 sensor 2...replace cat converter a year ago..just had problems with misfire codes 0401 or 0301 mis fire in cylinders..random..only put about 30 on that code before i got it fixed..just picked car up ..drove about 20 miles and now i got the 0420 bad cat again..any help sugeestions recommendations..agh.....

Asked by for the 2001 Toyota MR2 Spyder
P0420 is a code for catalyst efficiency, usually requires converter replacement which can be costly.