2011 30D feels like its slipping between front and rear wheel drive

[Nick1975]

Hi, I bought a 2011 x5 30d 3 weeks ago but have hardly used it until last week when i took it on a bit of a road trip. Until then all my driving had been on country roads up to speeds of 50mph. On the trip last week when on a motorway and accelerated from 60 to 70+ there was a noticeable splutter as if it had a misfire. I then noticed that it got worse when going uphill on cruise control.
Having read all sorts of forum posts I am now thinking it might be the transfer case. When I turn tightly in a parking situation I can feel the tyres working against each other as I used to on my Vitara 20 years ago. At first I thought this must be normal on an X5 but the forums say otherwise.
What do you all think?
It was bought from Evans Halshaw not BMW, has a 2 year warranty so I could try to go that way and get it repaired and as yet I have not told them about the issue.
I love the car but I am now worried in case there is a significant bill round the corner.