need help with po code

[1iwilly]

ok i'm running of thing to look for for this dam p2096. quick recap.1 1/2 month ago did a head gasket job had a crack between intake valve. so all new gaskets and seal were replace and a new CCV+new hoses new throttle body elbow also the 2 lower downstream o2 sensors.today did a smoke test no leaks found. also fuel filter was change new plugs new coils been i had engine 1/2 apart why not do the pre maintenance at the same time.been previous owner neglected all that. when i clear the code it doesn't pop up until i have driven over 40 mile distance.any body else that had this issue i don't see fix mention any help would be more than appreciated thanks