Cummins isx 450 , very good engine, powerful, good fuel economy, around 7.2 mpg during the summer 6.7 on the winter, hauling 43000 lb . Empty is about 8.5-9 mpg , bobtail around 12-13mpg. Engine has 1.68 million miles. Overhaul was done at 1.45 million according to previous owner. I will email full service records per your request. New tires, breaks, drums, driveshaft, center bearing , wheel seal, new oil in transmission, differentials and power steer, etc.