Would have to be a 2.84 gear but speedo may be reading a bit high - is that the MPH you read from the OTC (would expect 1450 to be more like 53) or the speedo. Our 88 has a 2.97 gear and pulls an incline smoothly at 1300 rpm in 4th/lockup. OTOH our '90 SE does not engage lockup until over 50 mph so never gets that low.
Both cars have been upgraded to Delco ignitions, the '90 after it began chuggling a bit on inclines.
This is the secret to MPG - turn the engine as slow as reasonable. In the bad old daze the 400 in my station wagon was turning 3200 rpm at 70 and that was with the economy (3.0
axle. At cruise most of the gas was going to pump air through the engine and accellerate the pistons.
Waaay back when we had the first "gas crisis" I got a '67 327 Camaro close to 25 mpg at 70 with very tall (28") rear tires, a 3.31 gear/Muncie trans (no torque converter loss) and mechanical FI. Was an experiment but possible. Today our cars have smaller air pumps, better aerodynamics, and much more control.
Now if all of you driving is stop and go city, 16 mpg is not unusual but even our 3800 TranSport gets 22-23 mpg on a 9 hour 600 mile run (one gas stop and one rest stop) .
Don't forget there was a National Speed Limit in the US of 55 mph when our cars were designed and built, no wonder they perform best in the 50-65 mph region and not to shabby aeven above that.
And if really low RPM is your goal, don't forget that one of the fastest steamboats on the Mississippi, the Robert E. Lee, developed 15 hp at 44 rpm.