2009 Jetta SE 2,5 Dropping RPM when breaking/slowing down and then bouncing back on 2009 Volkswagen Jetta

I took my car to service at least 3 times, They couldn't figure out what was wrong with my car. They always come up with , My car is running as its designed no problem answer

My Car 2009 Volkwagen Jetta SE 2.5 liter.

I am using Plus Gasoline,

Here is the problem.

1- Whenever I drive over 40 and when I start to decelerate my speed then car's rpm is dropping below 10 suddenly and bouncing back where it was before. Then sometime car jerks.

Also I tested this way,
- When I slow down I switched gear to S(tiptronic) and found out car gear is not going down fast enough to catch up slowness, like car is going with 40 but gear is still in 5 or sometimes 6,

Asked by for the 2009 Volkswagen Jetta
bring it to a tranny shop for diagnostic run. general mech. shops(or dealership shops for that matter) some times aren't as well equipped to diagnose or trouble shoot tranny issues. tranny tech.s are specialists. tranny tech. will advise.