P0430 code set 3 months ago, reset ECM and now code is consistently reappearing. I have seen threads on this, but involved some modification with headers and exhaust replacement. Every thing I have is stock. 101,000 miles current. Light originally triggered around 85,000. Will replacing down stream O2 sensor cure?

 

replacing the O2 might not cure it but it might if thats the issue. It also could be worn exh manifold gaskets, broken manifold bolts or pin holes in the exh.

 

May seem like a stupid question... Would a bad gas cap cause this issue? Also, Is it common for a 4 year old truck with very high mileage to develop a bad converter?

 

bad gas cap would cause a EVAP code but not emissions code.