My question is this.
what's the 0-60 time?
your vehicle may not have the HP to climb the hill due to timing, injector, or alda issues. do you have a cat on the exhaust? possibly a brake caliper is dragging?
MB designed the vehicle to have a specific ratio, and changing it of course will have effects, if your car cannot climb the hill,(what's the grade and duration of the hill?) something needs to change. either the HP needs to go up, or the speed needs to go down, or the ratio needs to be shorter, or the tires need to be smaller... I vote HP...

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!