The D100 was the lighter-duty model, while the D150 was the heavier-duty version. This meant the D150 had a higher GVWR, allowing it to carry a heavier load and tow a heavier trailer. The difference in payload and towing capacity resulted from differences in things like axles, springs, and sometimes even engine options. The D150 typically had stronger components to handle the increased weight.
Beyond the payload capacity, there might have been some minor differences in trim levels and available options, but the core distinction was always the weight and hauling capabilities.
