Hi, I am new here and I would like to ask you for help, I have MB clk 500 w209 year 2003.

The car shifts hard when driving and shoots into high RPMs during kickdown, but the car does not pull as it should
(accelerates very slowly) it also sometimes happens that when reverse gear is engaged, it takes 5 seconds for the car to start moving and then the engine warning light comes on. When I turn off the car and start again, the control disappears but the problems persist. The fluid in the transmission changed 7,000 km ago and everything worked well in the beginning. I hear no sound or creaking.

any ideas before it goes to the mechanic again?

Thank you in advance for your help and I appreciate it very much

You'll find lots of threads here (sadly) about transmission troubles here, for example: https://mbworld.org/forums/clk-class...ues-p0715.html

If you want to become more knowledgeable about these cars a scanner is a valuable tool, also mentioned in this thread. Even if you never turn a wrench on the car yourself
it's a good place to start.

722.6 in general is very reliable transmission (especially mechanically), but there are two common issues which might happen to it:
1. Faulty conductor plate. Easy to replace (unlike in 722.9)
2. Leaking transmission connector which could cause problems with TCU (sounds strange but transmission crawl by wires and get to TCU which is inside the car ). Usually it's enough to replace the connector and clean the TCU from transmission fluid.
But scarlettdave is right, get a scanner, one of the best is iCarsoft MB II (MB Start is better, but it's in different price range ).