Huge change in fuel consumption?

I own a 2007 f-150 5.4 triton v 8 I have 28000 mile tires are inflated correctly and all the little stuff is taken care of ie oil change ect. Ihave seen a reduction in mpg a slight miss at idle and sometime the oder of gas while at idle. I use to get 17mpg in town and 21.5 on hwy now 11mpg in town and 17 on hwy. Thanks jim

There are no codes. I did a live data read on the 02 sensors and Bank 1 and 2 upstream have fluctuating readings with a square up and down sign wave but Bank 1 and 2 downstream are reading 0.000. I would think 0 reading would show a check engine light are is this reading normal? I have 170,000 on the original 02 sensors so was thinking it might be time to replace.

Additional information: I drove around with live data and both bank 2's started giving readings. The sign waves where all over the place and at times flat lined.

Both downstream sensors started responding.

Haven't changed anything, truck is stock. The mileage drop off has been last 4-5 months. I was reading where 02's can become lazy and not throw a code causing a drop in fuel economy and with 170,000 miles on original 02's I thought it might be something to look into. The truck has been very well maintained.

Thank you for the response, looking into to doing that.

2002 F-150 4x4 Super Cab 4.6L V8
53,000 mi
Auto Trans
Tires 265 75 16 (Originals 245 75 16)

Bought the truck used through a non-Ford dealer and also purchased a warranty plan from the same dealer. The head leaked in January, and the dealer replaced the gasket. In March, it started to leak again, and they told me this time that the cylinder head itself was gone. They then installed a new head. Now the truck is low on power, and fuel consumption is up by 25%. On the highway, the tranny often shifts itself back into 2nd gear just to keep 65mi/hr on the hills. It was never like this before. I brought it back and they are now telling me that the problem is with the tires, that they're too big. They also said the truck needs to be "recalibrated" for the tire size. But its only one size (as stated above) and I had this tire size on the truck since last fall, and also the winter before, with no problems. Any ideas or suggestions are greatly appreciated. Thanks.

Thanks for the reply. Went back to challenge the dealer, and they finally gave in and sent the truck to Ford. Turns out 2 cylinders on the right side (same side as the new cylinder head) are 6% low on compression. Looks like I have a legit case. Again, appreciate the second opinion 2CarPro Jack!