Hope this is the right place to post this question.

I have a 2006 C230 with about 55,000 miles. Lately my car would not go more then 40 miles an hour and if i keep gassing it the rpm can go up to 4 or 5. What i would do is shut off the car and remove the key. Then it will work again without any issues. I notice when i reverse out it will make a clunk sound sometimes. This always doesn't happen but it happened and with me removing the key and starting it again didn't work. I sit in traffic a lot so my car stop and goes a lot.

The check engine light pop up for the first time for this issue. I was wondering if anyone have a idea what is going on? I know if it's a blown transmission it's going to be very expensive.

I also swapped my transmission oil a few weeks ago and prior to this it was already doing this. I didn't have the transmission filter swap.

Any advice would greatly be appreciated.