Loss of steering when making a left turn

I was driving my truck, made a left turn and when I expected the truck to just stay in its lane and go forward, I realized I had no control over the vehicle and it was behaving as if I had hit a patch of ice, which I hadn't. I braked, put it in reverse to get back in my lane, then drove it immediately to the dealer. They found nothing wrong with the steering or?

I did have have the power steering motor replaced earlier in the summer but then the fluid leaked out and it was very hard to steer. This problem was just the opposite. Complete loss of control of the truck for a time.

The tech at the dealership tested my truck and couldn't duplicate the problem.

Any thoughts?

Thank you,