For the last year my mileage has decreased from 14.5 down to now 12.1 I have ran RP oil up until abot 100 miles ago then I switched to Penn Platnum. I have 33000 miles now. I have the same driving habits as always. I keep the tires inflated to 35 lbs. I always keep clean air filters. Do you guys think it could be the o2 sensor or do any of you have any ideas. I have a 05 kc 4x4 big tow.