My 190 has a similar problem, regardless of the temp if have delayed and very hard shifts until the car warms up and even then the tranny shift hard, with a thud going into 3rd. Also it seems as if i have very serious throttle lag when accelerating however when in park or neutral the engine seems to have no lag but thats with no load on it. This past summer I changed the ATF fluid and filter and that seemed to improve things but only for about 2 weeks tops. Either in the next month or next summer I will be having the transmission looked and and worked on if need be by the dealer. I described the symptoms to a friend of mine and he suggested a broken torque converter could be causing this. Im not sure if this fits your problem but a torque converter is alot cheaper than a new tranny

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1984
190e 2.3L
107000 miles