My car, a 96 C280, got the ATF changed at 80,000 miles 2 weeks ago. After changing the oil (with MB's tranny fluid), I noticed the car was shifting rough so the fluid was drained again and replaced with another 8 quarts and that seemed to fix the problem.
However, a couple of days ago something weird happened:
I was driving at around 45 mph and tried to overtake someone. I pushed the pedal half way through, and the transmission downshifted to 3rd gear which seemed stranged to me as it normally takes more gas to make it do that. After doing that, I stopped before a red light and when it turned green and I tried to accelerate, the revs went up to 4000 rpms quickly even though I was slightly pressing the gas pedal and the car moved very slowly (worn clutch effect?). I immediately went to an MB shop I normally go to, and when they test drove the car it wasnt doing that anymore, instead it was shifting extremely rough. They adjusted a valve that regulates the oil pressure on the transmission and that seemed to fix the problem, until I drove it the next day.....
Now, the car works flawlessly while its cold (And lasts like that for around 10 mins), but when it fully warms up the transmission shifts in a very aggressive way from 2nd to 3rd (Like someone hitting my car from behind), and moderately hard from 3rd to 4th.
I was just wondering if anyone has gone through this and found what causes this horrible shifting.

BTW, I went through all the transmission threads that popped up with the search button and I couldn't find definite answers.