Since we had no idea of the maintenance records concerning this thing, we gave it a tune up. Plugs, wires, cap, and rotor all got replaced. The button in the cap was worn through the brass and the gap in the plugs varied 0.060- to 0.090-inch. We went from a solid 16 mpg on the highway to 17-18 mpg. The next weekend we replaced the engine oil, transmission fluid, transfer case fluid, and the fluid in both differentials, but noticed no difference in economy even though all the old fluids were filthy.