Sensors :: 1998 Chevy Cheyenne C1500 4.3L V6 - Codes P0420 And P0131

1998 Chevy C1500 4.3L V6 170,000 miles

My truck is stumbling and losing engine power sporadically. When this is happening I can usually drive it if I am real easy on the gas and slowly build up speed but if I mash it the engine will eventually just die completely. It has had this problem off and on for several years and now it's back with a vengeance. It always seemed to happen after a heavy rain but now I'm not sure.

Last week I had a mechanic look at the codes and he cleared them saying that once it happened again the code(s) that showed up would be a good indicator of the actual problem. The codes that were there were for a couple O2 sensors, catalytic converter and loss of vacuum I think. It happened again and his shop was closed so I got it read and cleared somewhere else and it was P0131 bank 1 sensor 1 and since I knew that one had come up before I went ahead and replaced it myself.

The next day the CEL came back on without any noticeable engine trouble. That was yesterday, this morning it rained and the problem is back and I went to get the code read and it was the P0420. There was also C0281 stop lamp circuit something or other that was new.

My gas mileage has stayed pretty good this whole time, always 15+mpg. Just wondering if my catalytic converter probably needs replaced, if I should replace other O2 sensors, or if this all might indicate something else in the engine.