Limited slip additive, is it needed with Royal Purple?

I'm currently swapping out my 2.73s for 3.73s. Normally you would put regular oil in and add some limited slip additive. Is the additive needed with Royal Purple Synthetic oil?

I do not believe you need to add an additive with Rpurple. But you do with Red line.

Unlees it specifically says it is in their fluid, I would add the GM posi additive.

I think that RP does mention that it is in the fluid but when I put it in I also added the GM additive and so far so good for the 2nd year running.

Thanks a bunch, guys. I'll relay the info to my friend who's doing the swap. He's got additive and regular oil if it doesn't work out. :)