Some manual transmissions don't like to be towed even in neutral, as the counter-shaft will not turn and stir up the oil to lube the turning output shaft. If in doubt and it's a short trip let the truck idle in neutral while being towed, this will ensure the transmission gets oiled.
If it's a long tow, and or not running then pulling the axle shafts (3/4 ton and up) or removing the driveshaft from the rear axle is a good idea.
Grigg
