That mileage is normal for the stock Fiero 3 speed TH125c transmission. It was designed to operate best at 55mph back in the 80's. You can put in a 4 speed auto, or switch the car to a manual transmission, but that's a lot of work to save a few mpgs.
edit...you could expect about 32mpg highway from a 5 speed on the V6.
[This message has been edited by Gall757 (edited 02-03-2015).]