Toyota Repair: CEL and 2 rough starts, o2 sensor, tune ups

Question
My 2000 4Runner v6 3.4L auto 4wd SR5- Check Engine light came on yesterday morning when out of the blue the vehicle started up rough like it was missing. Did this 3X. The vehicle was recently purchased from Calif. owners took car in for regular tune ups and maintenance- well cared for. It ran beautiful before this spontaneous malfunction. ~117,000 miles.
I took vehicle in to Toyota service.  O2 sensor seemed to work okay and they thought it would require replacement of the 2 cat converters = $2000.00.  We question this.  what do you think?

Answer
Before I can be of any help at all I need to know what the diagnostic trouble codes(DTCs) that are that triggered the check engine light, cat converter problems on V-6 engines are not very common so let me know what the codes were and I can go from there.