Don't underestimate what looks to be a small difference. I didn't look up the original tire size for a v6 for my year. In my case (according to Tirerack.com specs), my 225/70-15 Generals were around 27" and my 235/75-15 Kumhos were around 29" (just working from memory right now). I remember when checking on the exact sizes they showed, I was running about 1.05 larger tires. It can make a difference. In my case, I average roughly 25 mpg unadjusted. 25 * 1.05 = 26.25 Not too big a deal, but 1mpg is 1mpg (or 1.25 in this case). For some of you who may be running 33 vice 31, you could be looking at the same type of correction. You're likely already taking a hit in aerodynamics and overall tire/rim weight, no point in adding an error. My $0.02 or $0.021 if I use the correction.
2004 Frontier, King Cab, XE, 4-cyl, 5-spd, 4x1