The 18" wheel shares the same bolt pattern as the 17", so it will fit the hubs, but the offset is much larger. The front hubs were different on the 1-ton trucks with the dual wheel option to account for the increased wheel offset, but the rear hubs were the same. Are you planning on using duals in the rear, or just using the dually wheel as a single (mounted as an outer) for the look? Either way will cause fender clearance problems if your truck has a pickup bed. If using a single dually wheel, you may be able to compensate with a narrower rearend, but it's probably not appropriate to use a single high offset wheel as it would put unusual stress on the hubs. It would be better to modify the 18" wheel to match the offset to the 17's.
