Duh, limited slip additive does not make the clutchs slip easier not at all, it helps the clutch pack to lock up better, that is what it is for and it's only purpose. As for turning 1 tire if it is a govenor stye posi it needs pressure and speed to actually lockup, it won't turning it by hand only clutch only types do this. As stated by all the real only way is to pull the cover and at least you can inspect the oil, the gears and for posi when apart. Rip it apart dude, and if it is a posi and the oil looks good (no shiny flakes of clutch material) then use additive with the diff oil or it won't work properly. Good luck. By the way really nice truck, only see 1/2 tons nice to see a 3/4 ton.