Okay, I am starting to get pissed about my mpg in my '11 5.0 s-crew 4x4. I keep reading how people are getting 15mpg city. I'm steadily dropping and currently at 12.6.

I put in a K&N intake
I drive 90% city and my commutes are between 10-15 minutes long to and from work.
My tire pressure is at 37lbs on all 4.
I use regular gas
I drive under the speed limit more often than over.
I accelerate slowly and coast often.
I have not tried any fuel injector cleaner but was going to pick up a bottle for my next fill up.
I have a tonneau cover covering the bed

What the hell is going on? Why am I getting such crap mpg? What else should I do/check?