Thanks for all of the replies!
*when purchasing the tires I was aware of the extra weight but was still somehow hoping to do a little better around town. But not a big deal, we are happy with it. We took it up to the mountains on a sharp rocky road and we were glad to have solid tires.
* My F-150 has the max tow so it does have the 3.73. I think the Whipple tune and 91 octane helps the mpg.
*Today we did 17 mpg @ 80mph from Holbrook AZ to Tucumcari NM according to the computer. I was dumb and forgot to manually calculate. I will pay attention tomorrow and post that data.
* I am also interested to see difference in mpg between 70 mph and 80 mph.
*Are the factory tunes optimized for mpg or are their after market tunes that might help? The tunes more or less just change shift points and timing or is their more? Could a tune optimized for this larger tire size help? What about better air intake?
*Also if all factors remained the same what do we think the difference in mpg might be between 3.31 and 3.73 axles?
Overall I realize the expedition is heavy and the wheels/tires are heavy. Considering the hp these motors produce and how good these drive I feel like I should be pretty happy with m current mpg. Thanks again for the input!
I have the readylift kit with LT285/60/R20 Open County MTs and 3.31s. Turned a big, heavy brick into a bigger, heavier brick. I don't recommend it, and I will go down to a 275/60 non E tire when the time comes if I don't trade first.
With my setup on 93 octane, 10th gear is completely worthless so I lock it out, and it's in boost over 70 most of the time in 9th gear unless the road is very flat. Around town I like to drive in tow/haul mode otherwise the shift points are too low.
I will disagree with LCG on octane; anecdotally 87 octane makes me start going into boost just maintaining 60mph in 9th. I agree though with regards to the higher speeds, and it's even more pronounced with the lift and running larger tires.
After 30k miles, I'm averaging 16mpg with mostly rural 2 lane roads. By comparison, my leveled '21 F150, 3.5EB, 4x4 3.55s LT275/65/R20s is averaging 19.4 after 37k miles. F150 weighs around 800lbs less IIRC.
Grabbed the below values off a texas tech page, and assuming the values are correct this chart gives an idea of speed vs drag.