Re: LOW MPG, should I change the O2 Sensors?
A few things, FWIW. Are your winter tires the same diameter and approximately the same weight as the stock tires/wheels? Is the tire preesure set correctly? Did this all start around September/October and/or when you installed the winter tires? Remember, winter fuels normally don't deliver as good fuel economy as summer blends. Are you using a different brand fuel, and has it been reformulated and/or does in contain ethanol?
Bottom line, I wouldn't jump at changing the O2's unless you have over about 75K on it. IMO, there are plenty of other things that should be investigated first. I had one go "lazy" on me at just over 60K, so I replaced them all. You may want to check out the thread I did when I began questioning O2 Sensor integrity: Oxygen Sensors and Their Role in Engine Management--A Primer
05 LX/RT & 06 WK/GCO, modded similarly, MDS "ON" Light, Vortex Gens, Debadged, DashHawk, BT Catch Can, SRT CAI W/Add Air Inlet, K&N Filter, Sonnax Trans Press Booster, SC Tuner W/Adv Trans Tuning App, DS Tuner, Cust tube headers w/3 in. catback, Bilsteins, SRT frt/rear bumpers, Eibach SRT Lwr Sprgs & Sways, FRI Sidewinder Cam Adv 2*, 6.1 valvetrain, SLP 25% UD Pulley, BBK 90mm TB, SOS Coils/.060 plug gaps. 20 in. SRT Reps.