[bandit0067]

Thanks Palf, I was thinking there was some additive or special formula in Dexos 1 that those engines operated better with. But its just GMs brand of synthetic oil. Well , you will not get that from the owners manual....they scare you pretty big into thinking big problems if one uses another weight or brand in this engine. PO of the truck used independent oil/service businesses and did not know what they used, syn or non syn.