Limited Slip Issues

[935.0]

Every time in the past week that i have gotten wheel slip the truck jumped a little. It wasnt until today i realized what it was like because i was on wet pavement making a left turn and accelerating moderately and it felt like the factory limited slip was grabbing then letting go then grabbing causing the truck to jolt. I have had the diff fluid changed in the last couple months and i do not think they put friction modifier in. Could that cause the problem i'm describing? And if so where is the fill plug on the ford 8.8