I have a 2008 S crew cab, 4.8 with 67,000 miles that has always got good mileage, 16/22 mpg. Now it's only getting 12 mpg around town! I don't know why because it's running smooth, not skipping, no hesitations. I have started to get a little whiff of a catalytic converter smell occasionally but not bad. Does anyone have any ideas? TIA!