The mechanism to make a shift soft when the truck is accelerating under power is the trans letting the clutches slip a little by applying the oil pressure a little bit gradually. We all know what happens if you slip the clutch too much though. It's a trade off between the wear & tear on those clutch packs and the wear & tear of shock loads to the drive train from a hard shift. When they build a transmission for drag racing it's pretty close to full pressure right away-partly for speed but also partly to avoid frying the clutch packs.
The drilling company I worked for had 40+ trucks that went out at 45,000-50,000 pounds and often pulled a trailer weighing just under 10,000. They mostly had the Allison HT 750 and we kept the shifts pretty crisp because we ran heavy. If running light/empty, then a softer shift for comfort might be preferable. We've had some of the big trucks for 10+ years and never had to replace one of these transmissions, although we didn't put the sort of miles on them that a trucking company would since we would drive to a job site & be parked the rest of the day. We also had quite a few of the newer electronic models -the 3000 series- in smaller trucks.
We had good mechanics, but we usually took the trucks to an Allison specialist if something needed tweaking, especially on the electronic ones. It's usually pretty reasonable if they are just diagnosing & making some adjustments. The challenge is finding a good Allison shop near you.
