If the motor is Eaton, chances are the gearbox is, also. Unless you can find a tag with a model number somewhere, finding any information on it might be difficult. I used to drive an old 3-axle Freightliner with a 270 HP Caterpillar 1674 engine, a 5 speed transmission, and a "3 speed" Eaton rear end. The thing was actually two 2-speed rear ends in tandem, and the "intermediate" speed was obtained by shifting one axle to low and the other to high ratio, and letting the inter-axle differential split the difference in the gear ratios. It was also electric shift.
Jerry
