I know there's a lot that goes into gas mileage. Where do I start? I have a reasonalble? rear end at 3.7 and my tires are radials p235/R75/15 on original 15 inch rims. I'm about 3000 rpms on the freeway but keep up just fine, doesn't seem too stressed. I still have the original 3-speed transmission (on the tree). I was hoping to do better with a new edlebrock carb(600cfm- settings out of the box)and matching intake manifold. I have set the timing of the new HEI distributor with vacuum gauge and light. currently about 8 degree BTC since it doesn't start well at 4 degrees. I think I was stupid and let someone talk me into a different cam that was supposed to be better at low end range and be OK with gas mileage. I think that is why I can't get my vacuum above about 12 inches at idle? Is that my problem? I saw the recent posting about setting timing at a faster rpm with a vacuum gauge and thought I should try that. I like driving the old truck but what kind of gas mileage should I be getting?