Thats would be about 31.5" which is not much different than a 275/65/18, about a half inch smaller. So it would not be too much different than the stock tires. I dont think it would look too small, but I would personally go a little larger than that, but for you that means a different tire or wheels.
MPG loss = minimum to none.
The .5 smaller tire will not make much of a difference at all. According to tire rack they give an approximation of revolutions per mile. Both size tires were both spec'd to 660 (I am sure there was some rounding in there). I would not worry about either issue.
I have a friend running that size. They look fine. It's basically a 32x11.50-18 tire. If you level the truck, I'd go a little larger.
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2001 GEN III Supercrew, 4x4, gry interior, power bench seat with lumbar support
MODS...3" Body Lift, 315/75-16 BFG AT KO's on 16x10 Eagle 102 rims, Access roll up tonneau cover, tinted windows, chrome Westin nerf bars, SVT Lightning taillights, Pro Comp ES3000 shocks, Superchips tuner, Pioneer speakers
2005 Expedition, white Eddie Bauer Edition. MODS: 305/45-22 Falkens on chrome 22x9.5 Eagle Alloy 026 wheels, 20% window tint
if its leveled it will look too small. If its stock you should be fine. I have pics of 305 60 18's in my gallery in nitto terra grapplers. My truck is leveled. That will give you an idea.
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