Catalytic Convertor

[buxboatboy]

I have a 2000 Ex Cab 4x4 V8 105,000mi that has had the front O2 Sensors replaced at least 2 times by the dealer, last June the check engine light came on and the code said right rear o2 sensor bad, I replaced it reset light and had no problem till a week ago, the light came back on now the code says "Catalytic Convertor efficency" anyone see this or have replaced a Cat?

thanks