My 2004 ML350 downshifts to hold my speed as I go downhill too. I was surprised the first time I expected to pick up speed as I coasted down a big hill and had the transmission downshift.

So far as I know all the transmissions on the gas ML's downshift automatically to maintain your speed as you go downhill. I don't know about the diesels but it probably is the same. I believe this feature is covered in the manual.

I know I have the 722.6 transmission and you have the 722.9 but I believe the feature is on both.

Joe

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2004 ML350 Black with charcoal leather, OEM Hitch, Rhino step, Bose, Navigation, OEM front guard, Comfort package, Entertainment package, Sunroof, heated seats.