My mercedes will not shift down while driving. The faster I go the higher the rpm will rise and won't shift back down. For example if I'm driving 40 mph the rpms are at 4000 rpm. Other than that it drives great doesn't slip or anything. Also it has a slap shifter and once it goes into drive you can't shift it into lower gears its like it gets stuck.but it goes from park to reverse to nuetral to drive just fine