My guess would be intermittent vacuum leak. You've got codes upstream and downstream of the engine all related to fuel/air mixture. Check for a loose or cut hose around the intakes. I think it's unlikely the gaskets are leaking unless you've had the manifolds off or have overheated the engine. If you run rich you can burn out the cats. Then you'll really loose power as the air won't flow through them any more. If all else fails, may want to consider a compression check on each cylinder to make sure it's not something really bad.
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