Sounds like your toe-in is off. Was the alignment done with a spreader bar? This should always be used in conjunction with an alignment it that it duplicates the outward thrust action your front wheels do when driving.
You might also want to check the rear suspenion thrust links. These can cause a wandering feeling, especially at speed.
Have you replaced your front and rear sway bar bushings? Although these probably are the reason for your handling problems, they are inexpensive and easy to do (DIYer job) and make a difference in flatter corning and transitions.
Keep us posted,
'03 E320 Wagon-Sold
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'65 911 Coupe (#302580)