What kind of gas should you use for a 1998 dodge ram 1500 4x4 5.9L?

A 1998 Dodge Ram 1500 5.9L should use unleaded gasoline. The owner's manual will specify the octane rating recommended, likely somewhere between 87 and 89 octane (regular or mid-grade). Using a higher octane fuel won't hurt, but it won't provide any performance benefit in this engine. Using a lower octane fuel *can* lead to knocking/pinging and potential engine damage.