Yeah, we said "fun." We didn't really expect that an overdrive button could be so cool, but it was a blast to chirp the tires by clicking it on. Likewise, turning it off on the highway, into a non-overdrive passing gear, was a thrill, too. And the icing on the cake: blasting through all the gears, splitting them with the overdrive (that's six in all for our Turbo 400-equipped Chevelle). It was so fun, we almost forgot the initial impetus for going overdrive: better gas mileage.
A careful measure of fuel economy before and after the Gear Vendors installation revealed that even under ideal conditions (55-mph top speed, no full-throttle blasts), the best we could muster on the highway without overdrive was 7.5 mpg. After the install, we easily pulled down 10 mpg, and we were going way faster than 55 mph, more like 65 mph. That's an improvement of 25 percent. Put another way, we could go the same amount of miles from our fill-up for about 20 bucks less-and still have 5 gallons left in the tank. The only question we're asking now is: "Why didn't we do it sooner?"