Mercedes transmissions use a throttle valve cable and kickdown solenoid to control shift timing in relation engine load. However, working pressure and shift feel are controlled by modulator pressure which is influenced by engine vacuum. Do you have the correct vacuum modulator and has it been adjusted properly for your vehicle application? There is a stamping on the trans case on the passengers side just above the pan rail below the B1 servo cover. After the first ten numbers there will be a 722, a space, and then three numbers right after the 722. Either beginning with a 3, or a 4. This would tell me which modulator is required and what the correct adjustment relating to modulator pressure will be for your particular vehicle. This is where you need to begin before any further diagnosis.