I experienced the same thing, so what we did was change out the entire front suspension, (thank you FCP Euro!) for the 10pc kit, with two front wheel bearings as well! completely eliminated the shaking under braking! and handles like a dream! these SAV's are a bit more complicated than your average chevy, and they handle ALOT better than the chevy! the down side is they are a bit more complicated to set up and require a bit more attention to detail, just think, when youre apexing a corner in your chevy, do you often find yourself thinking, hmmm wish i had the bimmer instead!
Happy new year!
good luck

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2003 X5 3.0i (02/2003) sport package, Sapphire black metallic / Black Dakota Sport seats. compass mirror retrofit, trailer hitch retrofit, Prodigy P2 trailer brake controller installed, PDC retrofit, Lumbar support retrofit. heated rear seats retrofitted. Running boards retrofitted and subwoofer install in progress. 4.8is Brakes installed front and back. Bluetooth TCU installed, Rear Fog lights installed. Retrofitted reclining rear seat backs.