Having an issue with my trans. The car has 208k on it. New engine but trans and torque converter are stock. New Mercedes fluids after motor rebuild 6k miles ago.

So the issue. Originally after the rebuild all was well until I had this slip between 3rd and 4th gear upshift. When going to 4th it would over rev, I would have to let off the throttle and then 4th would catch. Today since it got really cold its gotten a lot worse and now over revs/slips as soon as I give it any throttle. I take it my torque converter is shot?

Thanks for any help or input.

The tranny is on the way out.