Dino is what comes in it from the factory, synthetic is required for towing heavy loads. I use Mobile 1 75w-90 and it has really dropped my oil temperature, might be worth you mail ordering some. Sometime back, there was a post from a member who told that Eaton would extend the differential warranty from 100k to 700k miles on over-the-road trucks if Mobile 1 was used. I stongly suspect that Mobile 1 is repackaged by DC and sold as their "house" synthetic lube. Some use Amsoil but it is pricey and difficult to find locally. Maghytec sells LE oil ( I think) but pricey and have to mail order it too. Hope this helps.