Tom,
Having never used RP, I'm only familiar with Amsoil.
On the label it says: "compatible with petroleum fluids"
And here is a statement from the RP website: Max ATF is fully compatible and can be mixed with other automatic transmission fluids; however, for the best results drain or flush the current oil and then fill with Max ATF.
Here is a link to the RP site: http://www.royalpurple.com/
A little snoopin' around there, should answer all your questions...![]()