I am currently looking to replace my Mercedes 99 ML430 with either a Sequoia LTD or LX470. Your vibration problem caught my eye as I have the same problem with my ML. It normally comes in around 105kph, but seems to go away when you get closer to 140kph. It is not a problem during single-passenger travel, but is noticeable on my way to the cabin during which the vehicle is loaded with 4 people and luggage.
Mercedes has driven it and say that they amount of vibration is normal for a vehicle of this size, but rebalanced, realigned etc just the same.
I have noticed a similar effect on a Nissan pathfinder, but not to the same extend. I think it may have something to do with the size of tires (seeing as the ML has quite wide 275s), but I could be wrong.
Anyways, I hope you resolve your problem. I will be sure to look for it during my test drives.
