5th is one to one in the manual, should be what they used. I wondered if you still had your mustang Toothless... Figured you went back to a Camaro. I did find a 1LE 15 that I've been thinking about..... Thanks for the comparo.
Another thing to consider is that numerically low rear end gears tend to dyno slightly higher (unless you're using a load dyno and holding road speed steady) because the less gear the car has, the less most of the drivetrain has to speed up to produce a given increase in wheel speed. This means less losses to inertia simply from the engine revving up faster andthe transmission internals and driveshaft speeding up faster. That was in favor of the auto car in this case, so the percentage of drivetrain loss difference just between the two transmissions might be greater than this test showed.