Had the stupid P0420 code for some time now, but I've always been able to shake it... until recently. Knowing that there could be many causes I stopped by Monro Muffler and had them hook it up to their computer. Told I need new cats... When asked how much they charge for one they said they replace the whole y pipe and that runs $975 (summit sell the whole y pipe units for around 470). I know cats can be cut out and welded in (even though they said they can not) what would you all recommend? New cats or the whole y pipe unit itself? Since they need replaced I was thinking of just going with magnaflow or flowmaster highflow replacemets. Thanks all!