Sometimes you can weed out problems by staying on schedule.
We have seen bad Air filters, fuel filters, and dirty throttle bodies causing random misfires.
P0420(bank 1) + P0430(bank 2) Low catalyst
9X's out of 10, it's a bad cat!
Have a local muffler shop do a free inspection on both cat's, if the
cats are bad, consider OEM from
http://www.catalyticconverterwarehouse.com ,and
have the local muffler shop do the install.