I wonder if your transmission is not downshifting. If the engine is smooth, try:

Manually dropping into a lower gear, and see if the performance doesn't improve.

If it does, might be a bad kickdown switch or misadjusted linkage.

If your used to a Stage 1 GS, this car will "feel" slow. Compared to my 83 turbodiesel, they feel "ok"......

Jim

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14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles