I keep getting lean codes. Which computer part do i need to replace?

What is your question?

I had a new catalytic convertor put in, vacuum hose is fine, new spark plugs. Everything possible was done. I know I need a new computer board, but not sure which one. Also, am I safe with a used one, or should I purchase a new one?

What makes this problem better or worse?

WORSE: Accelerating on highway, or long highway drive

How long has your 2006 Subaru Outback had this problem?

got the car 2 years ago, every since I got it. Intermittently