Having gas mileage problems. Rough idle, wasting feul. Getting around five miles par gallon, feul odor in cab and blow by. Gas "smoke" exiting exhaust tailpipe. Has converter, has O2 sensor above converter but NO vacuum line to it. Cant find vacuum line.
Where does it go? Need help!

 

You probably have a hole or holes in the muffler causing fumes to go into the cab. Or possibly the pipe cracked at the muffler. It happened to me recently and smelled like fuel in the cab as you described.