Transfer Case
 

Does anyone know if the transfer case can have something to do with the gears slipping when turning?

maybe its your cv joints that are shot.

Gears slipping as in the transmission not holding a gear? Didn't you just change your transmission fluid?

@jcl, yeah i had the fluid and filter changed and it helped a little but the x was slipping already before i had it changed. I had it done at a shop and now the x just slips when i turn a corner, the guys at the shop test drove it and told me that it was the transfer case maybe low on fluid or needed a fluid change, im not sure exactly...
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Does it feel like slipping when you take off from 0kmh with the wheels turned, or it also happens when you turn any corner at any speed? Might be the dif.
Also, if it was the TC, the car would act like that on straight lines too. TC fluid getting old throws an error on the tester - oil abrasion on the VGSG module error memory report.

@chas3, i feel it when i turn and take my foot off the gas and then step on the gas again while turning, the engine would rev and then it feels like somthing hit me from behind.

What year is your X5? I thought there is a recall on S/W update for trans on 2005 and newer, for that "rear-ended" problem. I'll contact your dealer to check on that recall, I can be wrong though.