Get a synthetic brand of your choice in a 75w-90 unless you want to loose around town MPG. Once the axle is up to temp, there is an almost undetectable increase in MPG, but around town you will thank the 75w-90. If you are towing, racing, have some monster HP, or have a strech limo, then by all means a 75w-140 may be the better choice. But for a daily driver that sees normal driving, the thinner is my choice. Also, if you think about it, why did all older 8.8" axles come with 80w-90 dino gear lube? If 140 was really needed, wouldn;t you think they would have used it years ago?