Here is the deal... I also have a thread running on QW relating to this topic but want to check if the community here may have some ideas..

CEL comes on anywhere from 65 to 100 miles.. Codes both are referencing post cat failures... One engine bank running lean and one running rich.

Exhaust setup is APR downpipes and magnaflow the rest of the way back. I did se that APR replaced the cats in their downpipes back in Dec 07, so I wonder if there was a similar issue with the older cats. Anyone remember hearing of post cat issues with the APR downpipes or have any idea what could be going on?

All sensors appear to be fine as well as injectors so the CELs keep bringing us back to the exhaust system..