2003 Suburban with check engine light on and now says reduced engine power. Had code read a few days ago and it said "mixture too lean" on both banks. Tech said it could be MAF or O2 sensor but probably the MAF. I replaced this about a year ago and bought some cleaner and cleaned it. Light has remained on after approx 200 miles and the display just started saying reduced engine power.

Does this sound like an O2 sensor problem? How hard are they to replace myself? Is it ok to drive with this message for a day?

Thanks for the help,