So today I'm in my car complaining to my buddy that I can't make my USB drive shuffle play and press the random button on the head unit to prove that it doesn't work in that mode and........ Suddenly it works and I now am listening to random/shuffle play of all the music on my USB stick. It even randomizes the folders while it's randomizing the songs. I was a little surprised when it jumped genres from a Stevie Wonder song to Tool.
Now if I could just figure out why I was never able to successfully do this the hundreds of times I tried it before I would be ecstatic.