The car jerks into low gear with a loud thud and jarring motion when I slow down going into a turn. The shifting is very rough but not reliably reproducible. It has done it repeatedly, however, since I started driving the car and it was brand new.

This happens sometimes when making a turn at low speed going from 1st gear into 2nd gear you get a bump from the transmission. Doesn't do it when going straight from a stop and speeding up. Doesn't always do it and I can't make it happen.