Wow, that brings back the good old days of driving myself through college. I worked for a small local outfit that had several Diamond REO COEs, one with the Fuller twin-stick and a couple more with the vacuum-shift thumb-knob on the disk-like shift knob to go between ranges - I believe those were 12-speed (H-four pattern times three). Shifting the twin-stick was always an adventure in contortions. Hold the steering wheel with your left knee, lean over to the right and shift both levers with both hands. It wasn't so much that you needed speed, but you had to feel what was going on in the gearbox through your fingers and know when everything lined up and then slip it into gear, all without the clutch.
The vacuum-shift 12's were a whole nuther thing. Get rolling with the clutch in 1'st or 2'nd (depending on the load) and then up/down shift with no clutch after that. I drove a summer later on in an Autocar with the vacuum 12-speed and it was like heaven. Sweetest gearbox I remember. The engine rpm gaps between gears were all pretty much equal so you shifted, no clutch, simply by watching the tach. Once you got a feel for the tractor you did everything by sound/feel and reflexes. The gearbox (at least for me) never "ground the gears" - It simply would fight against you going in to the next gear which you could feel in the shift lever and never forced it. It would just glide into gear or it wouldn't but you never forced it and simply could not "speed shift" it.
Never drove a Mack Maxi-Dyne 4-speed, but understood that the torque band was super wide and the truck performed more like a gas job than a Diesel. Macks and Maxi-Dynes were mostly bullet-proof and seemed to last forever. My town had a 50 Mack that they recently sold to a collector and it was still being used by the town up until five years ago as a specialty rig.
That summer driving the A-Car was a hoot. Some local guy sold an entire hill to the Mass. Port Authority to expand Boston's Logan airport. He leased 8 A-Car dump semis and moved all that dirt into Boston. If it was a good day (no flats or breakdowns) a driver could get in four trips per day (2 hour round trip plus 30 mins at the airport plus 30 mins to reload). This is how they expanded the airport's "Terminal "B" - that entire end of the airport is built on fill, just like "Back Bay" Boston. It got so hot that summer that the trailer tires were melting from the heat and load and would often explode the sidewall away from the wheel. Sounded like a damn cannon going off. One truck's tire did that right into a Chevy's rear door, severely damaging the car.
For several weeks, there was a lot of work going on on the Mass. Turnpike into Boston and they had 3' tall orange cones set up for traffic control. We found that if you flew by at the right speed and spacing from the cones you could get them to flop over. That, until the Mass. DPW spotted us doing that and the cops started fining us $25 per cone flopped over - Cash, on the spot, or we couldn't continue. That stopped us right there.......