Sorry for the long story. I don't want to miss any detail as I ask for help.
In September 2018 I was driving from Indiana to Wyoming. Indiana elevation of 1,100ft, Wyoming elevation of 10,000ft. In Nebraska (4,000ft elevation) and on the interstate, my 2006 Pathfinder started chugging like the gas tank was empty and stalled at cruising speed. I had a full tank of gas. After pulling off the side of the highway, I turned the key off and restarted the engine. The Pathfinder started up ok but the Check Engine Light came on immediately. I tried a few of the things I read to reset the ECM, but the Check Engine Light always came back on immediately after starting the Pathfinder back up.
I decided to not bother with it until recently because the fuel milage decrease is annoying me (18mpg to 15mpg even when I got home to Indiana). I recently changed out the rear O2 sensors on Bank 1 and Bank 2. While I can get the Check Engine Light to clear and not come on immediately, it does come back on at highway speed with the same P0420 and P0430 codes.
For those with more experience, should I be looking at changing A/F sensors on Bank 1 and Bank 2 next? Can catalytic converters fail instantaneously like that and they be the root cause?
Thanks for the help. 2006 Nissan Pathfinder with 145,000 miles on it.
Tony