Fix the stuff that's obvious, then come back.

The PCV hose on most of these modular engines connects to a port that faces the firewall and is a challenge to get to.

 

 

 

The lean codes can be caused by an air leak at any point between the throttle body and the heads. I always start with the simplest and least expensive fix first, then work "up" from there. Since you are throwing codes for both banks, it is most likely at or near the throttle body or the intake plenum. Did you check it for cracks when you replaced the gaskets? A disconnected or broken line between the Idle Air Control (IAC) and the throttle body will cause the lean condition too. While I've never heard of an IAC sticking open, that is another possibility. I know they DO stick shut. mine requires cleaning about every 100,000 miles. I pull the throttle body and clean it at the same time.

 

Actually, the correct span would be between the MAF sensor and the heads. The MAF sensor is "upstream" from the TB.

Vacuum leaks in the intake tract probably account for > 90% of these code pair occurrences. MAF sensor issues and fuel supply issues take care of most of the remaining.