MAT Replacement

Hi,

You all helped me replace my abs module after I bought my car last August, now after having all the plugs, coils and boots replaced I am getting a lean run code on both banks of engine. Car runs well until accelerating hard and hit 4000+ rpms, any gear....

So far I am getting told cats / exhaust, which I was told last year and not the case, or MAT, however, I am being quoted 500 bucks to replace a $65 part. Is this something like the abs I can do myself.

Thanks
JB