Timing a 99 318

Be patient.....I'm new to the site and new to owning this 99 Ram 318. The gas mileage sucks and I've replaced the wires, plugs, cap, and rotor yet it's still getting only high 14's driving mostly highway miles. It's an automatic with a 3:55 rear ger 2 x 4. I bought a Haynes maunal but there's no mention of timing it. I know it's got a crank trigger but does this mean as the timing chain wears, there's no way to adjust the timing? Does anyone know how to time this or is it not possible or necessary to adjust it?
Thanks