There were some massive changes with the new 2020 Sierra HD and Silverado HD trucks, one of the biggest points of change was the upgrade from the 6-speed Allison transmission to the 10-speed Allison transmission. This will only be matched to the Duramax engines with many upgrades over the previous 6-speed transmission.
The 10-speed transmission has been developed by both GM and Allison in order to make it available for these trucks. The new transmission should allow for quicker and crisper shifts than the old transmission. This will improve the ability for the new trucks to get the power from their Duramax to the ground, with more torque being put to the ground in lower gears. The new standard ratio is lowered from 3.73:1 to 3.42:1 which enhances refinement and reduces engine speed for a more efficient truck. The transmission case is all new and has an integrated torque converter housing to increase overall structural rigidity through the vehicle's powertrain.
One of the new features also includes a factory integrated Power Take Off, PTO, eliminating the need for an aftermarket unit. The PTO is run off of engine speed allowing it to be used even when the truck is idling. A button inside the cab allows for users to adjust the load and torque output of the PTO.
| Gear Ratios :1 | Allison 10L1000 |
| First | 4.54 |
| Second | 2.86 |
| Third | 2.06 |
| Fourth | 1.72 |
| Fifth | 1.48 |
| Sixth | 1.26 |
| Seventh | 1.00 |
| Eighth | 0.85 |
| Ninth | 0.68 |
| Tenth | 0.63 |