Try this formula...It was one I found that I wrote down years ago. I had another one that used tire revolutions per mile but I can't find it.
(Maximum Engine RPM X tire diameter)
divided by
(Rear axle ratio X Transmission top gear ratio X 336).
So you have provided rear axle ratio and an Allison 545 has a top gear ratio of 1:1 so the bottom line of the formula would be (4.66 X 1 X 336 = 1565.76) so divide 1565.76 into the sum of the maximum engine RPM X tire diameter and you should have your maximum road speed in MPH.
Sake of argument if the engine is 4500 maximum RPM and the tires are 28" tall you would have:
4500 X 28 = 126000. Divide that by the 1565.76 and you have 80 MPH.
Not sure if U-Haul has an engine governor keeping it down to 3000 RPM but if so you'd get 53 MPH maximum with everything else the same.
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