I have a 2001 ML 320, and with the OEM shock absorbers, I was rocking like a craddle after 10,000 miles. Complains to the dealer and MB customer service were just a waste of time.
I got fed up and installed Bilsteans, and rocking was history. Handling is great with the Bilsteans, but if you are not careful with the correct tire pressure and torsion bar settings, your ride may become harsh or variable.
Remember that tire feedback is what adjusts the valves/disks on the shock absorbers. If there is not enough feedback then your shock absorbers will be soft and rolly.
First add pressure to your tires, if your OEM shock absorbers do not provide you with better handling and less rolling at low and high speeds, then you may need to install new shocks.
Remember that tire design affects the feedback passed to the shocks. Depending what tire design and materials it uses and, of course, the type of side wall: Michellin, B/Dueller's, etc. you may have to increase or decrease the recommended tire pressure to get the right high and low speed shock dumping performace and a smooth drive at all speeds. If you can only find a pressure that comfortably works only on low speed rides or only a high speed rides, then your shocks tuning is worn or may not be adequate for your setup and something may need to change.
I used to raise my front ML using the torsion bars, but that is a terrible thing for shock tuning. If you tighten your front torsion bars, then the non-linear restoring force of the torsion bars will neutralize the shock dumping capabilities and then you will be forced to add lot's of air pressure to the tires to increase the feedback to the shocks and increase their dumping effect, but then the ride becomes harsher and on very long drives you will notice difference on the shock efficiency and ride due to the extreme shock overheating caused by the increased dumping load on the shocks.
The torsion bars settings have to be correct, not to loose and not too tight. I never used to align my tires after adjusting the torsion bars, but at the end you will find out that if you modify torsion bar settings significantly, then you really need to perform a 4 wheel alignment.
My $0.02...
AC