i noticed with my 300e, the harder i drive it the easier it downshifts to first. when i put the pedal down half way at a stop it will usually downshift to first. if you "granny" these cars you have to floor it for first or manually shift.
the computer has some sort of logic circuit that compensates for the drivers needs of acceleration.
hope this helps.
good luck,
Adam

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Current Stable:
01 ML55 AMG
92 500E (a few mods)
87 300E (lots of mods)
00 Chevy 3500HD Diesel Box Truck
68 18' Donzi Marine
06 GT i-Drive7 1.0 Mountain Bike (with GPS!)

PREVIOUSLY OWNED:83 300SD, 87 420SEL, 88 420SEL, 90 420SEL, 86 560SEL, 86 190E 2.3-16V AMG, 94 E320