All my Mercedes diesels with auto have shifted to high at way to low a speed to suit me.. I started just running them with the shift lever in 3rd.. some are marked 2nd but are really third.. and shifting into 4th or drive when out on the road.. My 76 240 shifted into high at 26. 79 300sd at 24, 78 300cd at 24.. and 85TDT at 22 mph.. Living in hill country it was just not some thing that works well, so have been just shifting to drive when I am running on the highway or need it .. Mercedes says that is why the shift lever has no gate between 3rd (Marked 2nd on some cars and Drive..

While the kick down does work on my cars, I seldom ever use it and just make the shift down by hand.. I do notice the biggest difference with my 92 300 CE as it takes some time for the transmission to shift and seems to wait until the cam timing changes.. Making the shift by hand far faster.. I also notice the shift by hand works faster than the kick down on the 300TDT.. However its some thing we do many times every day we drive so we do notice it more..

Ken