The Allison 1000 is rated to handle up to 620 ft·lbf
(841 N·m) of torque. Initially it was a 5 speed
transmission, but a new "Generation 4" 1000 was
introduced in 2005 that added a 6th gear at the very top
of the ratio ladder, making it a double-overdrive like
heavier duty Allison transmissions. For the 2006 model
year, manual gear selection was introduced. This feature
gives the driver greater control over the transmission,
enhancing operation when engine braking or less frequent
shifting is desired.