Why the 10.5 over the 9.5?
I have 9.5(235/85r16) on my FJ80.
I was thinking about 16 inch rims. The 255(10.5 wide) is 33.3 inches tall, where as the 235(9.5 wide) is 32 tall. So the point with me saying go with the 10.5 is for the height. Also I think on a 80 10.5 inches wide would look right. My 9.5's are fine. But they are narrow.
My RPM with the gasser at 100-110 and my 235/85/r16 is right around 2000-2200 rpm . 3k sounds too high.
I would look at the rear end to see if the gears have been changed back in Japan for more bottom end. It may not be stock diff gears in your truck.