I notice a subtle miss between about 45mph and 60mph. Any ideas? Seems like I read somewhere that this was an issue with this van, and Chrysler didn't seem to know why. I tried high Octane gas, no change.

I had a simular problem as this - an occational misfire cruising at highway speed. The usual source of this type problem would be the plugs or the wires, but in my case they were new. The problem went away after I had the throttle body cleaned out with carberator cleaner.