Was Wondering About Changing Trans Oil To Spectro 6-speed At Next Service. Heres My Question,the Spectro Is A 75w140 Oil According To The Package,i Have Some Left Over Royal Purple 75w140 From Servicing The Diffs In My Truck Was Wondering If It Would Be Compatible Since They Are The Same Weight.local Dealer Dont Know Anything About The Spectro Oil,says Anything Else May Be To Heavy And Affect Shifting In Cold Weather,i Live In Northern Illinois And Typically Ride Up Until The Weather Changes Around Thanksgiving Time. Any Thoughts Would Be Helpful.