Do you consider that combination of engine, transmission, and chassis to be an efficient way to move rock. Overall cheaper cost of chassis and operation?I've got both Px8s and 9s. Ive had nothing but problems with the 8,s and no problems with the 9,s ( better knock on wood). They are in Kenworth tandems with the Allison RDS 3400s. Have had no issues with the Transmissions. I haul gravel with them.