Rock & Asphault Millings Driveway Problem - any suggestions?

Last year we built a new home. We have a 500ft driveway that leads up to it. Our contractor suggested a base of 3" rock and asphault millings on top to finish it off to make a nice level surface.
After the fall rain and winter snow thawing, we've got a lot of mud coming up through the millings. I made a few calls, and it seems the "norm" is to lay a 5-6 inch base of 3" rock before putting down millings...I'm told mud will come up through the millings if there is not enough 3" rock base.
Our contractor really only had a single layer of the 3" rock, so I think that's the root of the problem...not enough rock, and mud is coming up.
By the way, I'm in the Midwest (Central Illinois). I think certain regions of the U.S. use different types of rock, millings, practices, etc.
Does anyone have any suggestions as to what to do now? Should I have a layer of "driveway" rock layed down on top? Is there any special type of rock that might be best to lay over what was already (perhaps, poorly) done?
Any suggestions would be greatly appreciated!!
Thanks, Mike
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