Fuel Economy..?

I have a 77 d200 crew cab pickup with the optional heavy duty frame, slant six, auto trans. The Army ran it till they decided it was worn out, then it went through at least 3 businesses and 3 individuals before I got it. No sign the engine had ever been opened up, ever, and I was able to get a best of 17 mpg hwy. I never adjusted the valves, set the timing, tuned the carb., or even replaced the plugs. I averaged ~14 hwy/10-11 city in that beast and never lacked power to make things move! In a car you should have no problem getting decent mpg. Just my experience, your results may vary.