I have used the stock 4.11 1948 1/2 ton rear end, a 3.90 1954 1/2 ton rear end, and the 3.55 Patrick's conversion rear gears in a few 1954 1/2 ton trucks.
I had always thought that the 1st gear was for driving up the wall of a barn, or driving in a very slow parade, or winning the slowest truck race (at a show or fair). That is, until I had to pull a VW beetle out of a steep ravine (in 1970).
As stated above, 4th gear is 1:1, so your top speed is more a function of rear gears. The 3.55 conversion for 47-55 1/2 ton trucks is one way to get higher speeds (or lower RPM). You can easily cruise at 65 mph, and you can feel safe if you have good brake parts, and all good parts in the steering/front-end/suspension. And, you must have good adjustment of brakes and good adjustment of steering/alignment.
