Looking for better fuel milage

17 mpg out of a 72 340 w 355 gears is an bit of puffery...I had that same set up went up to 3.91 and back to 3.55 850 thermoquad and dynotuned at HUB's ( famous tune place back in the day)...never ever saw 17....maybe if you idle around and turn it off on down slopes ...beyond that somewhere in the 10 - 12 range..... so I would be interested to see your dyno specs... you may be running dangerously lean