1985 380SL Shifting problem
 

Hi, I've got a problem with my little mercedes. it's a 1985 380SL. it has 129400 miles on it. last week I was driving in highway "70 mph" and all of a sudden it shifted to third!! I released the gas pedal and it barely went to fourth and again after i pushed the gas it down shifted again. next day it was fine and i decided to service the transmission. so I drained the torque converter and transmission, changed the filter replaced the vacuum modulator and filled it with mercedes ATF. the color of old fluid wasn't dark. also couldn't find any broken piece in the pan. the problem getting worse. kick down cable works fine. please help me what else I should check before take the transmission apart.
thanks for your help

Sounds like K2 (4th gear clutch pack) isn't holding under pressure.

You can try increasing the modulator pressure.