A Group IV/Group V lubricating composition providing improved antioxidation performance comprises from 5 wt. % to 40 wt. % of a Group V base oil component, such as alkylated naphthalene, at least 30 wt. % of a Group IV base oil component, such as one or more polyalphaolefin base stocks, and from 0.25 wt. % to 1.5 wt. % of a trithiophosphate-containing compound. The trithiophosphate-containing compound is preferably C30H57O7PS3. The lubricating composition includes not greater than 5 wt. % of a Group I, Group II, or Group III base oil component, and, preferably not greater than 10 ppm heavy metal component. The lubricating composition preferably has a kinematic viscosity of from 20 cSt to 1,000 cSt at 40° C. and a viscosity index (VI) of from 130 to 200.