Bout 110-115 mph.
I'm sure you've done the math, but I don't think you are taking any wind resistance into account. Typically if you double the speed your wind resistance goes up four times as its exponential. I can tell you that I've tracked mileage many times and the difference between low 60s mph and high 70s mph is on the magnitude of 30-40% more fuel consumption, which supports this theory pretty clearly (clearly in my wallet).
I've got to side with Brad on this one: spend some time at the drag strip and you'll find out how accurate your seat of the pants dyno is (or isn't). I know the condition of an engine, particularly the fuel system, can make a big performance difference in these trucks, and some certainly run better than others, but I gotta say show me on an all steel cab and a half 4x4 cutting 10 second 0-60s. I have a ZF n/a 4x4 truck and I don't think I'd get 110 mph if I drove it off a cliff on Mt St Helens.
Just my .02.