Just got back from the trip.
It was raining the day I took it to the dealer, so they wouldn't ride it-no help. They replaced bad wheel bearings and I had them install a new front tire-same problem.
I'm going to check the fender bolts. It's hard to believe that could be it, but it's worth a try. Thanks SloChicken.
I'm also going to check my technique, oldbagr, because I don't remember if I was dragging the rear brake or not. Sometimes I do and sometimes I don't-especially if the turn is fairly wide.
Something else just occured to me along those lines, oldbagr. Whenever I'm slowing to a stop and I'm off the front brake and only have the rear brake applied, the bike "shudders" just as it comes to a stop. So if it's shuddering while I'm making my u turn, that may cause the wobble.