Still working on old junk. My truck has recently started to throw a consistent 2 trip check engine light, in addition to the periodic evap CEL. Inspection expires end of November. The evap CEL is so periodic that I can clear codes and get all systems to a ready state except evap which is always the last to clear, so 1 not ready = a pass for NY OBD2 tests. Did the after-cat exhaust on the truck a couple months ago. P0420 research has led me to believe it might be an exhaust leak before the 2nd o2 sensor. Climbed under the truck hoping to find a loose bolt right after the cat but before 02 sensor but no such luck. Second step was to start the truck and check for a leak. Very slightly exhaust leak right after the cat. A bit frustrating as I used all new gaskets and hardware on everything I changed. The flange after the cat is a bit worn away from rust over the years., so i can't really tighten the bolts down anymore, its already flange on flange. The last time I had the exhaust change for muffler I took it to a small shop that reused all the old gaskets and cross threaded things, but never had a P0420 with the orange permatex they used. I stopped at Napa this morning and got myself a new exhaust gasket, and also some high temp sensor safe permatex. The hardware is all new so it should be pretty simple to take out the 2 bolts, drop the pipe and inspect the current gasket. I might just apply a healthy coating of permatex and send it, or maybe switch out to the new gasket. I am pretty sure the new gasket I put in there was a cone shaped type, where as the one Napa gave me is the flat type. Just need to get it sealed up enough to clear the codes and drive for a couple days to pass OBD2 inspection. Anyone ever deal with one of these codes? Hoping its not going to turn into o2 sensors or an actual issue with the cat.