Having MPG issues, whats wrong?

But nowhere near as much as the rotational mass.
You're talking about maybe a square foot more of exposed tire which are round and decently aerodynamic as opposed to lets say 10-15 more pounds rotating on a 2" farther out radius that have to be pushed (per tire).

 

Nor7. Nice truck, cute daughter.
So many variables affect mileage, some under our control, some not.
I think fuel quality varies greatly around the country, and around the neighborhood.
Take good care of the cute little girl, and the truck.
My little girl, has a cute little girl of her own now.

 

stock size k02 no lift, no mods. 20mpg pretty consistent in the spring summer fall. 17 in the winter

 

I ended up going a different route. I went with Cooper Discoverer AT3's 265/75/16 Load Range C. They ride great and are not loud. MPG's have not been affected much.

 

I've been happy with my 07 DCSB V6 auto. It seems to hang around 19-20 combined, mostly interstate but I do have to get out of and into my neighborhood, which is a couple of miles from interstate access. I just drive carefully, as the v6 does seem to have plenty of low-end torque and on a typical day I will never exceed 2000, running about 10 miles at 70, then 10 miles at 60, but from those subtract the entry and exit from my neighborhood, so maybe 16 miles on interstate, 4 not. I have stock-size tires (Discovery LE I think) set at 33psi. Truck is getting better mileage than my old 2004 Ford Ranger, which also had a 4.0 v6.

My take is that it is not that hard to get the mileage to a decent point, and that it is VERY easy to drive it down as low as you care to see it go (just use a really heavy foot).

Certainly BFT's (Big f***ing tires) will cause MAJOR headaches. My son bought a dodge ram 1500 several years ago to use as a work truck. Bought it used. Had ginormous tires on it. Gas mileage (V6 engine) was horrible. We'd have celebrated 14-15. It was also so weak it would not pull even small hills on the interstate in 5th gear (was a manual). We eventually replaced the tires with stock and what a difference. Mileage jumped to what the EPA guessed, and it was now usable with cruise control on in the north-central Alabama area. Didn't look as "big truckish" of course, but in this case, form was much less important than function.