I drive my 1954 1/2 tons at 60-65 mph with no problems. It will be even nicer with the 3.55 conversion.
There is only one u-joint in the enclosed driveshaft (called a torque-tube) and they last OK (as long as the bell contains lubricant).
"Longbed" 3/4 tons (and 1/2 ton longbed GMCs) had an open driveshaft but had a small enclosed link/shaft between the transmission and the open driveshaft (47-54).
Torque Tubes from ChevyTrucks.org
Closed Driveshafts Forever is a Tech Tip on Jim Carter's Site (Tech Tips, 1947-55, Mechanical, Closed Drive Shafts)
