As I was retiring, I bought a rock bucket with an 800 cu in. Big Cam 400 hp turbo'd Cummins. Had it on a 15 speed tranny. Power band was about 300 rpm and it ran out just fine.
Since you were in and out of sand/clay/gravel pits with a full load coming out of the hole, one day I twisted the steel, splined, drive shaft and it broke, running between the tranny and the first drive axle. Engine didn't bat an eye.
To my utter amazement, I had no idea as to the tranny sync big trucks had but the only time I used the clutch was to stop/go.
You shifted by the tach. Ran her up to upper limit of the band, don't remember the rpms (1200 more or less), put slight pressure on the shifter with your finger and let off the pedal. As the rpms fell, the gears in the tranny lined up for a split second and she just eased into the next gear, no clutch, nothing but a finger's pressure and smooth as silk.
I was utterly amazed as the first thing I thought when I saw 15 gears was my knee was going to wear out with all that clutching. Not so.