Ever since I took delivery and updated my X to 8.1, I turned on all the new features and lane assist is one of them. Oh man, that was one scary experience. So I had a model S 90D as a loaner for over a month and I updated it to 8.1 with all the new features turned on, there were times that I felt like I completely lost control of the steering wheel when I switched lane on highway. When I tried to gain the control back, I fishtailed. So I think, no biggie, I should've blinked the signal. I did, and the feeling remained the same. OK, maybe it's just the car. Since it's a loaner, I happily returned it and picked up my X. Crap, the lost control feeling passed from the loaner to my own X. Then I thought it could just be the design and even thought I bring it back to service center, the tech would just tell me it's normal so I started researching on lemon law, buy back from Tesla or ebay it out. With such a low mileage, maybe I could've got most of my money back for a Porsche or Range Rover (sorry Tesla, bad influence from this forum...). All the sudden I thought of "Lane Assist", I immediately turned it off and started driving and changing lane. Voila, that was the culprit. Bottom line, Turn OFF Lane Assist if you feel like your car is losing control when switching lane.