I had a simular thing happen to me one time. I had just put together a turbo'd L6 and put my brand new Malvern Racing adj. cam sproket on. While driving around town to break her in, I hear and feel kinda the same thing you described.
Long story short.... the allen head fastners holding the cam gear together all backed out but one, and caused me to bend a few valves. Its a good thing I was only cruising at aprox 25 mph when it let go, or who knows what all it would have taken out.
It was my fault for not checking all the adj fastners before using the cam gear. I just assumed since I did not make any adj. to the gear out of the box, that they were tightened all up....
I ended up drilling holes in the heads of the fastners and running safety wire thru them.
Its hard to belive your timing chain snapped...