One day I got into the truck to drive and the wheel was all wobbly and loose. Had a 2 hour trip the day before and didn't notice anything. Overnight somehow it became this way. It's solid if I pull on it, but it flops around if I lift the wheel from the bottom using a couple fingers.

Update from Aug 8, 2018: The hexagonal steering column mates with a hex hole in the steering wheel, which flares/tapers out to round.

The hex hole in my steering wheel was not a tight fit, it was quite sloppy (somehow worn?) even when pushed onto the shaft. I slid a few thin pieces of metal in between and then tightened up the bolt that hold the wheel on. Used some loctite and I'm hoping it will stay solid.

In my case, the bolt was only loostened a turn or so, but because the shaft and wheel didn't mate well, it was immediately a very sloppy fit and the steering wheel wobbled about. (Some people say you need a puller to remove the wheel from the shaft... not me, it was loose and slid off really easily.