Check Engine Light going on - need some help

[USMC302]

172 - o2 Sensor sensor circuit indicates system lean (right side)
181 - Right side still lean, at richest adaptive limit, during part throttle
189 - Left side still lean, at richest adaptive limit, during part throttle

Definately showing a lean condition so we'll start with the obvious fuel possibilities.
When's the last time you changed your fuel filter?
Do you have any fuel mods, ie injectors, adj regulater, large fuel pump....?
How old are the 02 sensors, may be time to replace them.
Make sure your air filter and MAF are clean, if the MAF doesn't read all of the air coming in, the engine will think it doesn't need as much fuel going in, when in fact the 02 sensors are saying the opposite.
When was your last tune up?
Lsat but not least, have you made any changes at all before this started? Change octane in gas, use platinum plugs, anything at all?