2012 4x4 TRD Tacoma loosing gas milage

Looking for suggestions on what might be making me loose 4-5 miles to the gallon.? I have bigger tires but they have been on the whole time I owned the truck. I was getting 19 miles to the gallon now I'm getting 14-15. I replaced the spark plugs and seemed to help a little but not much. Any suggestions are greatly appreciated.

 

Sounds like a clogged catalytic converter.

 

Possibly winter blend fuel depending on where you live

 

^I bet there is some truth to this. My fuel economy has cratered in the last month. I rarely check my MPG's because I don't really care, but I am having to fill up more often now.

 

Yeah I love winter blend fuel the 2-3 mpg hit is great!

 

It was getting 19- 20 the first 2 months and the past 4 months it has gone down. (I have to keep track cause my wife complains about me driving my truck and not her car that gets better gas milage)

 

Wouldn't cataylatic converter make it run rough or thro code?