While the factory stock Allison 1000 is exceptionally rugged out of the box, several premier specialty transmission shops—such as Sun Coast, DTT, and ATS Diesel—build elite, heavily modified performance versions of the Allison 1000. These custom-built units feature upgraded billet shafts, heavy-duty multi-disc torque converters, reinforced clutch packs, and modified valve bodies designed specifically to handle extreme horsepower outputs generated by modified diesel trucks used in pulling and heavy hauling.