With 255/85's, bumpers, winch, suspension, protection and a spare tire on the roof I find that it really depends on speed. If I do 75, I average 14 - 15. At 55 - 65 I get around 17+. But I am overall a light throttle driver. Did great coming to NorCal today - it was all downhill 
Bone stock, I did regular trips where I was 22 MPG plus. (and yes that is converted to USA MPG).
So from my experience there is no single number for Tacomas. It's all very driver and mod dependent.
Pete
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/ -- \ Pete Hartl - VE6PGH - 0VRLAND
EXPEDITION = (Encounters + Adventures + Experiences) x YOU