Transmission Stuck In Gear problems of the 2011 Hyundai Sonata

For the second time, in interstate high speed traffic (70mph) the car without warning downshifted. A thunderous clunk is accompanied by the car lurching as it deaccelerates then almost immediately resumes speed. But instead of the engine being at 1800 rpm its closer to twice that. In both cases the driver behind me thought that I braked intentionally and nearly rear ended me. The car is then stuck in a lower gear and is driveable with extremely poor response. I had it towed once at the dealer's request and the last time I was able to drive it to a different nearby dealer to demonstrate that unquestionably the car was stuck in one gear. It is an automatic. I'm skeptical that either dealer has any clue to what is wrong. I won't let anyone in the family besides me drive the vehicle as I'm afraid for their safety. It has less than 7000 miles and is 8 months old. The first event was over 1000 miles ago and about 5 weeks earlier.

When driving at highway speed the car made a huge thud, it automatically shifted from 6th to 4th gear and remained stuck in fourth gear until you turn off the car. Took car to dealer and entire transmission had to be replaced.

I own a 2011 Hyundai Sonata se. 11000 miles. On December 11,2010 while on I-16 in savannah, georgia, I was driving my Sonata and it felt like my front end bottomed out. Rpms revved up and stayed at 5000 and I was only traveling at 65mph. It was like I was stuck in 2nd gear. Gears wouldn't shift up or down. This went on for 10 miles. When I slowed and accelerated it was very hesitant. I stopped the car and turned the ignition off for 20 minutes. When I started it again, it shifted normally. No other occurrences since then.

On 12/2/2010, I was driving at highway speed (approximately 60 mph) and the car violently jolted, as if I had run over a large object. If I had not had both hands on the steering wheel, I might have lost control of the vehicle. Subsequently, I was able to drive the vehicle, but it seemed to be over-revving, as if it was stuck in the wrong gear. I returned the vehicle to the dealership that night. After reading the computer error code, the service manager indicated that they would have to replace the transmission. I was provided with a loaner vehicle. On 12/8/10, I received a call from the service manager. He stated that in these circumstance, the transmission is typically replaced with a rebuilt transmission with a new housing. He indicated that the dealership was trying to obtain a new transmission for me. They were experiencing difficulty because there was 80 some requests for new transmissions and only 70 some available (county?, state?, central florida?) updated 01/20/11.