What gear is 1:1 on that car?

5th and 6th should all be less than 1:1. For reference, the Vettes have:
4th Gear: 1.00:1
5th Gear: 0.71:1
6th Gear: 0.57:1
with a final drive of 3.42:1

Ergo, *.overdrive gear ratios < 1.00:1 or it's not an "overdrive" gear ratio.

Also, accurate dyno measurements are hard to come by without a 1:1 ratio.