I,m getting 24 MPG in a 3,400 lb S/6 a-body with a 470 lift cam,3.23 gears,and a turbo. If your not getting at least 25 MPG out of a S/6 a-body car,something is bigtime wrong.Check for missconected dist. advance line,blown advance cannister(very common with S/6 engines leaking oil on pass side of engine),flooding carb,stuck advance weights.I bought a S/6 79 volare and discovered the advance weights were stuck.I ran into the prevous owner 6 month latter and he said he sold the car because of a lack of power,and poor fuel economy.He s#@t a brick when I told him I was getting 23MPG. Also, the first thing I,d check is those gears,you say its "screeming along at high way speeds"2.76 or 2.94 are what most cars came with.