I was driving my 2011 Optima with about 3,600 miles on it when I hit the accelerator to pass a car, I felt a big bump and heard a loud thump, the car was free revving and going nowhere. I tried to manually shift into gear and it thumped again and went into a gear, I tried to shift into another gear and more thumping and jerking. It finally locked into 3rd gear. I drove it to the Kia dealer. They confirmed it was locked in gear and replaced the transmission. After they replaced the transmission my mileage dropped by 10 miles per gallon. I now get only17 miles in the city and average 27 highway, combined city and highway 22. That sucks. I bought it for the gas mileage.