No I haven't removed the cats, if it was a sensor failure then wouldn't the ECU log it as that?

Both banks running lean makes me think they share the same problem....

It could be:

MAF
Split vacum pipe
Split PCV pipe
Manifold gasket leak
Fuel filter
Fuel delivery & injectors
Fuel pump
O2 sensors (if one out of four failed, surely it would only highlight one bank running lean / rich?)

Thats all