Sounds like the limited slip,
Im changing my fluid this weekend myself and im not putting in the friction modifier unless it acts up. Im using Mobil 1 gear oil though

 

Add the modifier I used amsoil when I bought the stuff I was told this stuff already had additive in it I found myself back under there the same day after a trip to the parts store adding the modifier anyway. After speaking with a relative who works for ford I was advised for my limited slip rear if I ever start to get a jumping sensation out of the rear to add a second bottle of modifier.

 

Well iv gotta buy a rebuild kit cause the spider has three tooth missing that was noticed and we went and replaced pinion seal and bearing and added Lucas 75-140 and the additive and it's still doing say thing so need less to say I'm sick



And that's the fluid and shavings

 

Well it was worse then I thought the spider has atleast three tooths missing so we ended up replacing the bearing and seal pinion and it isn't helped at all added 2 1/2 qurts of Lucas 75-180 and the additive so looking like heading to work in the morning and looking for a rebuild kit for the rear Pics