I just replaced the intake/exhaust manifold gasket on my truck and it starts easier, idles smoother and runs better but my gas mileage has gone way down. I don't know my exact fuel mileage, but before I was driving 225 miles on a tank of gas and now I'm doing good to drive 150. I had the carb and vacuum lines off, could I have crossed vacuum lines or leaks that are causing this? I haven't had time to double check this. Any input would be appreciated.