Got this from valient.org:
The Feather Dusters were made in 1976, with an aluminum inner hood, trunk bracing, bumper brackets, and intake manifold; economy carb and distributor calibration; large exhaust system; tall rear axle ratio; and either 3 speed auto or 4 speed overdrive manual trans.
Their gas mileage was great for their day, and even for the present, given their size: 24 city, 36 highway. Few modern cars of that size can claim this. With an automatic, gas mileage slipped considerably, to 22 city/31 highway - still comparable to modern cars. Very few were sold, partly because they had to compete with the new Aspen and Volare, which were in the same price class; and because the tall rear axle ratio took a serious hit on performance.