[Fulltiming]

Tom, Newell introduced the ZF transmissions (10 speed) during the 2005 model year although most 2005 models were fitted with the Allison 6 speed. The 10 and 12 speed ZF's, along with the Allison were available by the 2006 model year. By 2008, more than 50% of the Newells had the ZF transmissions. By 2012, more than 50% of Newells had the Allison again. When Newell began using the high horsepower, high torque engines, the Allison transmission was not rated to handle the full torque (over 2000 lb-ft) of the Cat C-15 engines so if you wanted an Allison transmission, an engine with de-rated torque (typically 1900 lb-ft or less) had to be installed. When Caterpillar was replaced by the Cummins ISX, the Newell specified engine generated 1950 lb-ft of torque and the Allison was rated to handle up to 650 HP and up to 1950 lb-ft torque. Now most Newells have a 600 HP Cummins ISX with 1950 lb-ft torque and use the Allison transmission.

Both the Allison and the ZF's are dependable transmissions. The ZF's have pro's and con's. If you travel extensively in the mountains, the ZF's give you more gears to work with and allow the use of the higher torque engines; however, the Allison's are faster accelerating from a standing start and are smoother shifting than the ZF transmissions.