I have a 1998 190e that shifts hard when the outside temp gets over 75 degrees, I'm assuming that at that temp the transmission temp gets high(?). I did have the tranny serviced but the problem still exisits. At temps below 70-75 the transmission shifts smooth. The Vac. modulator was checked and seems to work fine. The motor is a 2.6L and the hard shifting is between 2 and 3rd. Any ideas ?