Ill handling 900XP!

My 900 turbo is great until I really get on the throttle on higher boost, like above 6lbs of boost. It pulls nice for a bit then just carves one way or the other, it’s hard to keep it on the road. It seems fine on pavement or hard road but on gravel it’s swapping lanes like crazy. Very scary to drive. I do all my testing on gravel so I have to figure out what the heck is going on. Thanks, Dan