A p0420/430 is a particularly tough problem in the v6 as it doesnt point to any particular bank of catalytic convertor or any particular sensor failing. I suggest you download the manual and get familiar with a multimeter.
The problem could be in the heated oxygen sensors , the a/f sensors , the cats themselves or the ecm. Unfortunately the workshop manual flowchart if followed can lead to a very expensive exercise ie. they say if the sensors test ok replace both the cats , if that doesnt work replace the ecm.
Im sorry i cant give you a clearcut solution to your problem.