Hello. Thanks so much for the ideas. Those are the first concrete suggestions I've heard.
Actually, what happened was that the problem just seemed to correct itself. The day came when it just stopped doing it. My truck has 353,000 miles now! I expect the problem will return though at some time. We don't have harsh winters here, but maybe it had something to do with colder temps. So, maybe this winter the problem might come back.
My mechanic did tear out some wires from an old aftermarket cruise control that wasn't working that he thought might have something to do with it, but the problem persisted for a couple weeks after that, then went away. So, whether or not that had something to do with it, I don't know!
Thanks for your suggestions. Dan