Looking for Vehicle Advice

[JoeRaisin <joeraisin2001@xxxxxxxxx>]

My work van does something odd.

80% of the time, the van rolls straight and smooth but every now and
then it feels like the front tires are wobbling.  This is to varying
degrees - sometimes it feels like a little shimmy and sometimes it feels
like they are about to fall off.  This happens randomly on all manner of
road conditions but seems to be limited to higher speeds (40+) and more
often than not during acceleration.

The shop did an alignment and the tires have been balanced.  They have
looked at the front end and said there is nothing wrong - last time I
was told it was the tires picking up snow and ice but it happens in all
four seasons.

It happens on straightaways and on curves of either direction.  Slowing
down will stop it but it will also stop of its own accord after a few
seconds.  I don't think it has ever lasted more than 15-20 seconds - the
shimmy version if it, at any rate.  The more pronounce version ends
quickly because I will take my foot off the gas and reducing speed will
usually end it.

Any ideas?