[cdowns]

Originally Posted by Fitz

That is an Eaton Posi unit and they are quite adamant about the type of oil to use:

"Eaton Posi units perform best when using GL4 (or better) mineral/petroleum based gear oil. A four ounce bottle of friction additive/modifier is also necessary for optimum performance."

In short, do not use synthetics. They increase the clutch wear.

horsecrap why does gm come loaded with mobil one synthetic on eaton posi trucks from the factory from day one