Just applying 3,000,000 plus driven miles using direct and overdrive transmissions and recording fuel mileages along with a lot of other drivers doing the same and the results back up my statement. Overall a vehicle with a direct drive transmission and a 3.20:1 rear gear will return better fuel mileage than an overdrive transmission with a .76 overdrive and a 3.90:1 rear gear running the same speeds. Most engines have a sweet spot where they will consistantly return better mileage and my experience with the GM family of inlines is the 1800-2150 range.
Well if the A-833 OD would put me at about 2000rpm-2200rpm going 70, it seems like that would give me the best mileage since it's in your mentioned range
