Friction modifier and limited slip additive, same thing?

Don't get too confused. The RP should be just fine ... there are tons of people on this forum that use it in their differentials. When you drive your car, if the rear end 'chatters' then add some friction modifier. You shouldn't need to though. IMO

Mike could tell you for sure.

i thought they were the same thing

I really don't know. When I changed my diff. fluid, I went to Ford to buy some friction modifier. At the time, I had already bought some synthetic fluid that did not contain friction modifier. The guy at Ford said that the friction modifier would not work with the synthetic fluid. That confused me because of all the stuff I've read on here about RP (though that's not what I had ... I had Mobil 1). Long story short, I ended up using good 'regular' diff. fluid and friction modifier just to be on the safe side. But I've read tons of posts that say to just use RP without friction modifier.

Honestly and somewhat ironically, I trust some members on this forum more than the people at my local Ford dealerships. So all of that is what I based my post on.

Yes it is the same thing and RP is one of the manufacturers that adds it to the synth diff fluid so you do not have to buy it seperately.

In other words, you will be fine

Yeah, i used royal purple when i did mine too. You dont need the friction modifier with royal purple.