Im doing a lot of highway driving and with my shorter 225/50 15's the speedo has to read 82 to 75. Its killing my fuel mileage. If I drive with the speedo at 72 my traveler is showing that im getting 8mpg more on average.

Is there a taller transfer gear I can swap to? The tranny is from a turbo 87 J body. Would a omni or neon have taller transfer gears and if so how much would it lower my RPMs? I know going to a taller tire would be the easiest fix but I dont want to do that right now, as I will be putting on my studs soon, and they are short too. Going lockup would be nice... but not a option right now either.

I tried searching and couldnt really find the info I need.