I have a 5.0 '83 that the previous owner "rebuilt" the carb. Well, it would just randomly die so I purchased a new Chinese 2-barrel. It was running rich, adjusted the choke, and slightly adjusted the idle. Not running rich any longer and runs like a champ now. However, gas is between 9-10 mpg. With the old carb I was getting 12-14. I did a compression test and all cylinders were right around 120 except for one, which was coming in at 90. Timing has been adjusted, new spark plugs, exhaust leaks were fixed, and a brand new exhaust system (all things that were changed since buying the vehicle). I get this is an old, heavy truck but 9 MPG seems low. Suggestions?