P0420 08 128K with Cat Temps via BlueDriver

Hi All,
New to me 2008 128K Gen2 threw a P0420 code. MPGs are still fine @48.7. I was thinking it was an 02 sensor, but after reading a lot it may be the cat. I took it for a drive to get it up to operating temperature,I've posted some temperature readings from my BlueDriver dongle. From what I've researched, (Eric the car guy) The temperature at sensor 2 should be higher than sensor 1(to burn off the NoX). I'm just looking for confirmation that this is the case before I start throwing money at this. Any help would be appreciated.