My best has been one tank at 16 MPG at 100 degrees in Maine with 6 adults onboard, mostly highway, running with 3.73 gears and 32" tires.
Was seeing 15 and change on most other solo highway trips with same gears and tires.
For a 3 month strectch where I was driving it daily as my commuter car I saw an average of 11.5 to 12.5 MPG with mixed driving including about 50% interstate highway, same tires and gears as above.
With the 4.88 gears and the same 32" tires highways seems to be about 12.5 to 13 MPG, typical mixed driving is around 11 MPG.
Not enough miles traveled solo with the new 35" tires to have MPG data yet.
Worst mileage so far has been a tank or two at 6 MPG, that was with the 3.73 gears and pulling the 9500lb ToyHauler in the hills of WV.
Best towing with that trailer was 9.0 MPG with the 4.88 gears pulling from Savannah GA to Philly.
I run a set of Banks headers that I think have helped a small amount with MPGs. I also now run an SCT tuner from 5 Star Tuning, I think with the 87 Octane Econo tune and driving with a light pedal and MPGs in mind I can increase my base MPGs in mixed driving by about 1 to 1.5 MPG. Do as much coasting as possible, as little braking as possible, look waaaay ahead for slowing traffic or red lights/stop signs, accellerate very gently and the tuner will have you in OD and converter locked up below 35 MPH. Be willing to give up some speed on uphill grades and make it up on the down side. Driving like this is not easy and takes focus, it's hard to keep it up for an entire tankfull and it's not nearly as much fun as tearing up the streets!