I may hear some screams for this one, but here goes. We replaced the 90 wt gear lube in my dad's truck 4 speed with a synthetic (Amsoil I believe) oil of the same category. Awesome stuff. The old stuff was super stiff in the winter, while the synthetic was easy to work with. You could push the truck by hand in neutral even at 20 below. Gas mileage was better too. Any thoughts from the peanut gallery???
