Differential slipping?
 

I woke up this morning and my friend wanted me to take him to work as I went to my Dorm, and I was like sure.

He hops in the car and it was wet out, so I was like lets show him how fun mustangs are, cause he drives a golf. So I went to drift it sideways as I pulled out of his driveway and it one wheel wondered. I was like WTF.

Anyways down the road I tried it again and it failed, and I tried one more time and it did it, and hes like WOAHH that was awesome.

Well I dropped him off at work, and i start to head home, and when I get driving I tried to peel both tires and it did it, and I had to barely take off to keep from going sideways.

Is my new diff going out? Or does his weight offset in the passenger seat do something when the suspension twists? I do not have quad shocks installed.