If you question any of it, I would just run regular 'ol dinosaur 75W/90 stuff. But I have only used Royal Purple when using a TrueTrac. The TrueTrac is different cause it uses straight cut gears--The Eaton/Auburn uses clutches and bands...and if you use synthetic fluids, there is a possibilty of the clutches and bands of not grabbing properly. The Eaton/Auburn is kinda like our trannys--and I only use regular O'Reilly brand ATF.