[NewBayColony]

Those EZHaul trucks didn't have a tach so I don't know what rpm they were turning but they were fine at 65.I can't imagine it can be hard to find a ring an pinion for that. That is the trouble with old Fire Trucks. Most were geared very low. They usually are great trucks to buy. I missed buying my towns 56 FWD 1 1/2 ton forest fire truck because I had two kids in college. Some guy in the midwest bought it.
C90 Bill is right. You split each gear. Very hard to split first. Also it shifts much easier when you keep in in the mid rpm range. Don't rev it close to it's limit, it just makes it harder to shift it. When you up shift, you pull the button up while it's still under a load then just let off the gas for about 2 seconds and then apply the gas gently until you know it is engaged. When you go from say 3rd hi to 4th low, do the same but use the clutch until you get your timing down. the gears in the diff just have to be going the same speed to engage, Just takes practice.
One of my Ryder Car Carriers had an air two speed rear end behind a non synchro 5 speed. I enjoyed it.