A 2.94 would help. Alot depends on tire height. The 3.23 works great with two sets of tires and speedo gears for the trans. Like a 26 inch for around town and a 29 inch on long road trips. 25 to 28 inch might work better depend on the car body.
A 2.94 gear with 28 inch tires in back could maybe get 20 mpg @ 60 mph. Back in the 55 mph days we heard all the time how 70-75 mph was so wasteful compared to 55 mph. Today they just gear the heck down on the new cars. Like 2.94 gears WITH overdrive!